Check out Noah Surf House in Santa Cruz! The area has a super cool surf community (and the eco hotel I mentioned above) and is not touristy at all. It is like a less touristy version of Ericeira (which you should also check out- lots of great restaurants, hostels, surf culture, etc.).
Unfortunately the popular areas e.g. Lisbon, Porto or anywhere near the coast does not really qualify as low cost of living unless you are happy to share accommodation, otherwise it’s inland. The Algarve is very much an older vibe (e.g. retired) outside of summer.