A good cheap incubator for corn eggs is a Styrofoam (or plastic) cooler, water + water heater (or heat tape) controlled by a thermostat, some bricks and an egg box that will hold humidity. There are a few really good threads on that design, check 'em out.
There are lots of methods out there that will do the job though. Browse through the breeding/incubation forum and you're bound to find something you like.