I have - the cost of installing such a system makes it questionable if it will ever be worth it. I've seen a few places that have it and they work great year round and are cheap to operate. However the payoff from the install if 50+ years despite the cheap costs. Everyone hopes the install lasts that long, but a lot can go wrong in 50 years. (the equipment probably won't last 50 years, but that will be cheap enough to replaces, it is the pipes in the ground that better last 50 years)

A large chunk of cost is drilling the holes for the loop. New, compact drilling rigs that use 10' drill sections are a good deal cheaper to run labor-wise and require less space to maneuver. Costs will come down as more companies switch to these rigs.

What are some examples of these new drilling rigs?

The big cost for ground source HP, is the large area you have to dig with 4 foot deep trenches. I have seen one where the installer digs 2 trenches about 16 feet apart and 30 feet long down to 6 feet. They then use a soil drill to make about 50-60 holes between the trenches and insert 17 foot plastic pipes(1 inch diameter) They then connect the pipes on each side to a common pipe(3"), all well sealed ABS pipes below the frost line. This allow for a large volume of coupled and warm(55 degrees) that the heat pump extracts/deposits heat as needed for heating/cooling the home. This drilling is a lot cheaper than a dozen or more 3 foot trenchs for the water loops.

There's a reason NH is called "The Granite State."

Planning to put things underground in at least that part of New England is not likely to go very well. It can be done (plenty of places have septic tanks, for example), but it's not easy.

Unless you live in one of the few big cities in NH, you'll likely already have an Artesian (drilled) well. Swap out the pump for a variable speed pump and you should be good to go for a GSHP -- a much better option for NH vs an Air Source Heat Pump. Otherwise, it'll cost $15-20K for a well to be drilled. You get about 1-ton of heating/cooling per 100' of drilled well.

"Artesian" does not mean "drilled". It means the well emits water without pumping. You have to be downhill from the watershed for that to work.

You are correct! Around here (NH) the artesian nomenclature usually means drilled vs a dug well (i.e. a covered, but relatively shallow pit that fills up with ground water). The drilled wells are usually around 300+ ft deep and have a submersible pump near the bottom that is used to fill the pressure tank.