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).

Good question. It didn't occur to me to check. A bit of Googling suggests that in my state a new well would indeed have been less that 0.26 $H. At the high end of depth for this area maybe 1/3 of that.

I have no idea if it would have actually been possible, though. Wells aren't allowed to be too close to septic tanks and septic drain fields, and there are other spacing constraints too. From what I recall of the way the house was placed on the lot and where the septic tank and drain field were there may not have been anyplace on the lot acceptable for a new well.

Almost certainly-if any new well were allowed at all.

Could also have assumed that a well problem would entirely fall on you (worst case) and budget accordingly.

Good luck rolling that into your mortgage