You don't really need an incubator for corn snake eggs. That is, as long as you have a warm place somewhere in your house. Alot of breeders, myself included, just incubate their eggs at room temp. If there is a place that keeps the temp somewhere from 70F to the upper 80sF, that's your incubation place. On top of the refridgerator is good, as an example. I keep my eggs in the snake room, which is constantly maintained in the 75 - 88F temp range.
I use damp sphagnum moss in a tupperware shoebox with 1/8 inch air holes along the sides. The eggs are placed in the middle of the moss and I check the dampness every couple of weeks, adding water when needed to keep the moss at a "well wrung" dampness.
The eggs will take longer to hatch when incubated at a lower temp and not at the "ideal" 85F, but the only problem with that is the added stress to your patience!