You want something REALLY cheap? I put a one gallon container of top off water on a filing cabinet that is next to my tank (higher than tank), airline tubing, airline valve, suction cup holder for tubing. Put tubing into container (I actually use a one gallon water jug) down into the hollow handle, this holds tubing secure with end and bottom. Start siphon, attach valve, adjust drip rate with valve, hold tubing in positiion with suction cup holder. Add cheap funnel onto top to aid in replenishing water. Probably cost me $2.00 total.
It lasts 4 -5 days on my 10 gallon, keeps the water level pretty darn steady. No moving parts or electronics to fail. Yes I have to make adjustments once, maybe twice on the drip rate in that time due to either changing temp (controlled fan for evap cooling) or lowered water level in the container. But you kind of figure out the drip rate it will take and the adjustment takes about 20 seconds. To me simple is better, fewer worries.
Oh, forgot, also addresses your initial concern.
Edited by nhart608, 18 April 2012 - 09:12 AM.