I convert upright freezers into incubators. THe one I am using currently is 23 cubic feet. The insulation in a fridge is such that the temperature is extremely stable.
In most areas now folks have to pay to dispose of large appliances so you can usually pick up an old one for free.
I have a page detailing the conversion of the last one I did.
http://www.arbreptiles.com/cages/incubator.shtml
I've got $40 in that incubator, and I couldn't guess how many hundred leo eggs I could put in there, if I were breeding leos that is.
For lepoard gecko eggs you would do even better using a regular refridgerator with the freezer compartment. You can convert this into two seperate incubators. Calibrate the fridge section to your female temps and the freezer to male temps and incubate for both at the same time.