Hey Ugly (no offense),
Without living in San Sebastian myself, perhaps I can offer some advice for finding the information otherwise. Of course if anyone else who IS living in San Sebastian can pipe up with some better answers, please do!!
How much for a reasonable 2 bed apart
Probably about the same as one in Barcelona or Madrid, minus 10-20%. I’ve heard SS is pretty expensive all around however. In fact, in the summer it could be more than either of those cities, but the rest of the year a bit less. Check out http://www.idealista.com and search for “alquilar” “viviendas” “guip?zcoa” (the province) or “donostia” (the word for San Sebastian in Euskera/Basque). Also check out http://www.loquo.com
Wheres a good place (not expensive) to live in SS
I tried digging up some info here but without success. It would appear that the city is small enough that anywhere in the center of the city will be just fine though.