Yes, Donegal coastal properties have gone through the roof in recent years. You can still get good value (well, relative to prices elsewhere in the country) in inland Donegal. And by inland, I mean anywhere not RIGHT on the coast. You could be only a couple of kilometres away.
However you say you want to be near a surfing beach. Bundoran is Donegal's most prominent surfing beach (not a surfer, but AFAIK may be the ONLY surfing beach in DL?). Don't know your personal tastes but Bundoran would certainly not be for me, but you might find good value in nearby Leitrim, especially if you're prepared to go a bit off the beaten track.
From your original post though, Donegal is probably too far away for you.