When I looked for one, I found most started at temperatures in the 70s, and I wanted one that would keep water heated to the mid 60s in the winter months for standard ale brewing (I brew in the basement).
I went on-line and found one for about $15. I just checked the box, and it says "EHEIM Jager 3631" It is 75 Watts, good for tanks 16 to 26 gallons, and can be set for temperatures from 65 to 93 F.
I've never managed to get my fermenter above about 84 F with it. I think it is because I don't circulate the water as in a fish tank, and the top is open. 84 F is fine for me.
Hope this helps.