Hi,
I see a lot of recommendations for the ranco or johnson on/off type thermostats - they are around $70 - $80 I think.
A less expensive one would be the repti-temp 500 for about $25- $30.
Top of the line would be either the helix or herpstat proportional thermostats - I think those run about $120- $140 but I am not really sure.
You can see some of them on this site;
http://www.reptilebasics.com/Thermostats-p-1-c-250.html
dr del