While it's usually recommended to make your own thread, I'll offer advice here.
The cheapest recommendable thermostat is this. Why will you need several?
I'll always recommend Flexwatt for any situation. In my experience, a stick-on heat pad from the petstore and online that is about 8"x6" or so is about $24. I ditched them and bought three feet of the widest Flexwatt there is, plus the wiring clips, plust shipping and it cost a little less. I bought from Reptilebasics.com, and they will put the clips on for free. 36"x11" or 8"x6"?
A long strip of Flexwatt can be run on a single thermostat. So, if you're planning on heating a lot of tubs, it would be the way to go.
snakesRkewl, this was necroed from about three weeks ago, btw.