The cheapest route would be to keep it in a Sterilite or Rubbermaid tub. Upgrading to the next size enclosure wouldn't be a problem because each plastic box only costs a few bucks. If you were to get a hatchling corn, you can buy your supplies at Wal-mart for really cheap:
6 quart Sterilite shoe box with lid: 97 cents
soldering iron (for melting ventilation holes): $4.98
glass ashtray (for a water dish): 94 cents
aspen: $1.97 or maybe it was $2.97, I forgot
plug-in lamp dimmer (for the heatpad): $8ish
Then for a hide, just use a paper towel tube cut in half long ways, with a couple of small entrances on the sides. There's a picture of it in the Corn Snake Manual. This works as a great hide because the paper towel tube covers the entire length of the thermo-gradient, so your corn can hide at whatever temperature it feels like.
The most expensive thing will be a heatpad. You may have to spend $15-$20 for one. I recommend the T-Rex Cobra heat mats because they don't heat up as high as Zoomed. It also doesn't come with an adhesive, so you can just reuse it as you upgrade to larger size enclosures. Make sure you get a dimmer to go with it though.