I built a true cooler commercial glass door fridge into an incubator that will do 24 clutches for the same cost as that unreliably tiny incubator.
I wouldn't incubate ball python eggs in that unless it was given to me, and even then I'd have to use a good proportional thermostat on it.
I'm not sure there is a good incubator on the market for less than ...

http://www.nsreptiles.com/incubator.html