Figure a well can be drilled for a few thousand. Depends very much on the area though, some locations you can get plenty of water from a small hole not very deep (you can pound a pipe into the ground - with a hammer, put a pump on top and get plenty of water). Other places you have to go very very deep to get water and even then you have to be careful not to use too much. And there is all kinds of in between. Worse, sometimes one side of the lot will have plenty off water and the other will not. Then you have to watch for local issues, keep the well far from the septic system (including your neighbors).