I only do the refrigeration side of things and I don’t do residential stuff so I’m not sure on exact pricing. Pricing will also vary greatly depending on the exact area. For example in my area we have a high enough ground water level that open loop geothermal is easy and that is the cheapest/easiest method of geothermal. The other types will also vary in cost depending on soil type and moisture content because that will partially dictate how big of a ground loop you need. The amount of area you have for a ground loop will also be a big factor because if you don’t have enough yard area for a horizontal loop then you need to use a vertical loop which can be heniously expensive.

As far as payback goes they are far more expensive to install regardless of the type but the ground loop (assuming closed loop system) can easily last over 50 years and that is the most expensive part of the whole system by a large margin. Out of the $25,000 you mentioned I would bet that about $20,000 of that was just for the ground loop. The rest of the system is going to be more durable as well due to not being outdoors. The expected lifespan of the other components is 20 years and they can easily last far longer than that. So the energy savings is only part of the cost savings. The other part is that geothermal heat pumps need practically no maintenance and break down far more rarely than any other conventional heating or cooling solution. With how long they last and how durable they are a geothermal heat pump can probably pay itself off just with avoided service calls.