A lot of the cost is related to how deep the casing must extend. And that varies even in the same township. Sometimes you don't even know until the well is drilled.  I suggest find the most reputable well driller you can find in the area and trust him to do the job as required. They will generally give you a cost per foot on the drilling and casing.

As you point out, wells may be around for 60 years or more.  I would NOT ever have a well put in by the lowest bidder. jmho. Jim at Dawn