Try something digital, say an Onkyo WRAT receiver or integrated. May be more resistant to temp swings and humidity than tubes or traditional solid state. Sound decent too for the money. One of their recent 6XX HT amps could be purchased used for 200-300 bucks.
Or - look on ebay for any of the old Japanese solid state integrateds (Pioneer, Kenwood, Sansui, etc.) from the 70s - probably purchase one of those in working order for under $100.
Or - look on ebay for any of the old Japanese solid state integrateds (Pioneer, Kenwood, Sansui, etc.) from the 70s - probably purchase one of those in working order for under $100.