The OP is correct, there
IS something better and cheaper than the boating equivalent of an NCP car park. I will state for the record that as well as being a tight wad sailor I also vehemently detest marinas and
'let-them-eat-cake' marina developments in the UK.
The OP is looking for a cheap place to park in North Wales, well like houses you get what you pay for. North Wales is very popular with the Birmingham set and this demand has in some places pushed prices up. Unlike the south coast of England, the Welsh still seem adverse to fleecing their customers; accepting of course Aberystwyth marina, it is worth noting though, many many boats left Aberystwyth last year when they hiked the fees again...
Another difference to the South Coast, we don't have limitless funds and will up and move long before the pips whimper.
Porthmadog has been mentioned, which is where we tether the boat to the mud. We pay about* (er outdoors pays the mooring*) £600 all up for a secure harbour mooring (26ft), smack in the centre of the village. Even within a small area such as Porthmadog there are price variations (not enormous) dependant upon the type of mooring you can get. We are I guess on a half tide mooring, we never dry out but do touch bottom on springs. An advantage as we can always get on board by dinghy. Cheaper moorings completely dry out, nothing wrong with drying moorings, but these can leave you stranded without forward planning, i.e. you always need to be on the same side as your tender. Almost all the harbours are restricted by tides, but within the harbour some boats are always afloat, semi afloat, fully drying etc.
The walls at Porthmadog are owned by different people and wall moorings are available, but I would be careful which if any of these you might choose. The holiday tourists always tend to stay on the North Quays, this means a wall mooring on the North walls of the harbour will be subject to noise, trash thrown onto your boat, kids climbing on your boat and you living in a fish tank when on board.
The river moorings are favoured by many for privacy and better access at the ends of tides. There is another advantage in that they are not as sheltered from the winds, why is this an advantage, well, this is purely a personal observation from having my boat on all sorts of moorings around the town, I often don't know what wind there is until I am half way up the river, it can change from a lovely sunny afternoon to something rather horrid the further we progress to sea. Porthmadog does have excellent shelter, as it is quite a trek to the irish sea.
Now, being a lazy git, I will er on the side of caution and stay-in than go for a look-see only to turn back after an hours chugging out to sea. It is a pay off, one that I am pondering at the moment, we wake up in a beautiful harbour in the mornings, we can get on board in nearly all weather (only once said no in a full F11 when we were on the river, the boat was sitting fine, I just didn't fancy the tender). Since we moved up to the town moorings we have used the boat less. Even though the whole harbour is in-the-same-boat access-wise, i.e. we are all restricted to tides to get in and out, we did use the boat far more when we moored on the river. OTOH, Porthmadog is one of the prettiest harbours on this coast, many visiting boats come from uglier places to spend the weekend here, as we are already here, on a nice sunny day it can be just as pleasant to sit out and watch life go by.
We left Porthmadog for a while and kept the boat in Pwllheli, there are still plenty of small boat moorings available, especially if you can dry out. Prices are very much similar to Porthmadog and access is far better, 24hr on much of the harbour. Don't be frightened off by google only seeing the marina, contact the harbour master of both Porthmadog and Pwllheli for moorings availability (they often swap and cover for each other so most Gwynedd know all the harbours and availability of neighbouring harbours very well indeed) . Pwllheli is a particularly ugly town with little to do there, but as you are at sea within minutes of dropping the mooring strops, access is far easier with a much more friendly entrance, we did use the boat far more when we stayed there. There are many more facilities ashore, chandlers and yards, easier to get fuel (though PM has fuel, it is not as simple as Pwllheli as it means a trip by dinghy to the HM and lugging a can up, or going to the garage across the road, of course you can come alongside at HW, but I am a lazy sailor).
Cheaper moorings are available at mocras lagoon (shell Island), some are free if you put your own chains down. There is little infrastructure here and the entrance can be a right old git even in a moderate breeze. Shell Island all dries too.
Then there is Abersoch, in general these are absolutely summer moorings as most are extremely open. I am only guessing here, but I assume what you might save in mooring fees at Abersoch, you will make up for in annual craning, yard fees and insurance premiums compared to a more sheltered mooring (we stay in 12 months, though my insurance has *just* restricted me to 10 miles radius during winter, (fine as we only use the boat as a cottage in winter).
Another popular harbour is Barmouth, I like Barmouth once you're in, but the channel and sand-bar can be challenging, mostly in the prevailing winds. Barmouth probably gets most visitors from all the other harbours in the area, the atmosphere in Summer can be great... though I would say (IMO) Barmouth has the least shelter within the harbour of all the above places I have mentioned (except Abersoch). Many if not all the available moorings will dry out, I could be wrong, but the wet moorings always appear to be full. Though it is worth noting at this point, all the harbours in the area are council run and do run a fair policy of hierarchy, you start on a rubbish mooring and move up the longer you are there, rather than just flashing your wallet and going straight on to the best locations. This is not to be taken as dead man's boots, I reckon within 2 years you will be accepted as a local boat and be given refusal when spots come up.
The final location I will mention in this essay as it has turned out, is Aberdovey, a pretty seaside town more probably approaching mid-Wales in reality. Personally, I would not keep a boat there as the shelter is not as I would like, the prevailing wind howls down the estuary and after a night on board where we were taking green water over the bow on the visitors mooring (which had dragged) (F9 with a strong fetch) we had surfed over the sand-bar the previous day (not funny at all!) I will no longer entertain Aberdovey in anything but fine weather.. saying that, there are many local boats who obviously feel different.
Sorry to ramble on, I know big posts tend to be ignored, I am just writing stuff as I think of it.
As all the harbours in this area are council run, the costs to moor are generally very similar, the cost is broken down into harbour dues and mooring fees. I think our harbour dues are fixed at approx £140pa and then mooring fees will vary dependant upon location. Whenever we have moved moorings within the Gwynedd area, the difference in mooring fees has been so small such that we don't really notice it.
I hope some of this tripe has given you some ideas and I will happily answer any queries this may have raised, unless those queries refer to my metal health for writing such a long and empty diatribe
p.s. All the local harbours provide some dinghy storage, some have better car parking than others. All of them have local shops a walk from the harbour, many have larger supermarkets within minutes by car. If you sail from here, local boats stay in neighbouring harbours as visitors at reduced rates, for example, at 26ft we pay £5 per night to stay on the wall when we are visitors. We never stay on marinas (tight wad) even in Pwllheli where it seems visitors are supposed to go to the marina, we will raft alongside a local boat when visiting.. this is normal practice, I am always bemused when people go into Pwllheli as visitors and pay upwards of £35 a night when we are paying £5 for a more private and better view. I guess it depends if you are scared of tenders or not.
p.s. All my rambling assumes that you have a boat that takes to the ground, things get a great deal more complicated if you are the type of

idiot

that buys a keel yacht to sail one of the most tidal areas in the country, in some cases the planet.