I trust my home built incubators over one of those cheap incs any day and if you built your own you'd say the same I believe.

My first inc was a 4 cubic ft mini fridge and with 2 ft of flexwatt and a reptitemp 500R thermostat I had no problems hatching out a sweet group of yellowbelly's.
I don't recommend using an on/off thermostat, trust me it sucks!

A wine cooler with a fan and flexwatt and a good proportional thermostat won't set you back any more than the cheap pre-made incs and you'll have a better more stable incubator too.