control for attic fan
There are line voltage thermostats,  I use these for controlling electric heaters no battery a simple 2 pole switch with a temp dial. T522-w is the model I use 50-90 F temp range 120-240 at 22 amps 277v @ 18 amps I think it was close to 18$ at Platt but you may be able to find it cheaper online I believe when I ordered these there were some ~12$  but I needed 20 amp minimum 240V. , Added just checked online and you can find what you want using line voltage thermostat. Honeywell has one 13.95 (sold by Amazon) it's a 4 wire you only need to use 1 set, cap or tape the other set these are much heavier duty than your fan needs so they should last.