I have experience with geothermal on a commercial level. We did a project last year with 72 wells on it for a National Guard facility.
You muust have your soils tested for thermal conductivity, so are not as suited. If you have shallow rock, etc. that will be an issue. You will typically find that you need one 300' well for every 1.5 tons of HVAC needed. Costs of drilling vary widely. One concern in the midwest is that sometimes you may need supplemental heating, but probably not in a home.
You MUST make sure you use an experienced and reputable contractor. It is possible to "burn out" your site if it is not designed properly. In other words you must extract about the same amount of cooling in the summer as you deposit heat in the winter, otherwise you will have problems down the line.
Here is a place to start:
http://www.igshpa.okstate.edu/index.htm