I have an inexpensive one myself. It always seems to read within 1 degree of what my digital thermometer in the tank says. This is the one I have.

http://www.ebay.com/itm/290871141683...84.m1497.l2649

For those of you that have a Menards near you,They have one as part of their Black Friday sale tomorrow for 9.99

This is the model Menards will have tomorrow. Not much info on it though.

http://www.menards.com/main/see-more...96-c-13917.htm