The submersible fan I used is a battery powered "duck mover" that is basically a little submarine you strap to the bottom of a duck decoy so it will tool around the marsh and trick ducks into thinking the decoy is real. If you go to http://www.cabelas.com
and search for "open zone explorer decoy propellor" you should find it. $10.99 new. An ebay/amazon search for "decoy propellor" might save you money.
In regards to your temperature controller link via ebay...I cannot speak to whether that would be easier to use than my setup. I wanted to do everything myself, not buy a handy kit that I could plug and play. Other people may want less front end labor, in which case immersion heaters/circulators, thermostats, and various pieces of built hardware might suit them better. Plus, the main reason I used the Arduino was because I already owned it.
Good luck with your project!