I have installed several geo systems (for my small side business). 0Equipment prices have gone up in the last few years, with the material shortages and all. But it is still not that bad. A lot of guys dramatically overcharge for geo systems. The price can vary on the installation. A vertical well (closed loop) will cost the most. Average about $25K. It will fin on a small lot, but the driller gets most of the cash. You need average 150' of hole per ton. Usually 3 holes does the trick.
A horizontal loop is the cheapest. You need 200'-250' per ton. Deeper the better, but most go in at 7-10' deep. If you can trench it yourself, you can save quite a bit of money, and be installed around $10K average. More if someone digs for you. You need special equipment to join the pipe, as mechanical fittings are not used.
Open loop wells can be cheap as well if water is not too deep. They are the most efficient as the ground water is constant. However running costs do go up as needed to pump water out of the well. Also nearly all of the service calls I have done on geo systems are open loop, due to water issues. Dirt, scale, minerals and corrosion can all cause reliability and repair issues with the unit.
A couple of years ago I did a posting series on geo:
http://www.tractorbynet.com/forums/rural-living/74680-geothermal-heat-pump-project.html
You might find it interesting
paul