After seeing the other posts about it and pricing my own (no lower than $75) I thought I'd build my own too.
Waterproof box from Walmart $12
12v Cooling fan from PC power supply $0
Power switch from PC power supply $0
Potentiometer from an old CB $0
4 Bolts and nuts $0
4 Neoprene washers $1.52
Magnet from an old hard drive $0
AC adapter (12v output) $0
Beats the heck out of $75 to $90! All I need now is a stir bar.
Here are the results:
Top down view
Power switch and Potentiometer
Magnet glued to the top of the fan
Had to use the multi-colored ties, it's in a clear box!