Air-water heat pump current consumption and data

Including drilling only 1000 euros difference?
And yes, the COP is rather poor for a geothermal system.

I'll roughly estimate again in my head ... The drilling all-in was about €7800 (including paperwork, improved grouting material, sludge disposal, etc.). Of that, €4500 was BAFA subsidy and €500 funding from the state for the drilling.
The heat pump itself was about €1500 cheaper than a comparable air-to-water heat pump, which also requires the outdoor unit including installation.
So yes, somewhere in the range of a €1000-1500 surcharge - thanks to the funding.
The nice thing is, if the heat pump ever breaks down, you don’t have to spend money again on the heat source. Hopefully, the drilling will outlive me, which I wouldn't really expect from an outdoor unit of an air-to-water heat pump (mechanical component, weather exposure).

Yes, the COP is not very good. Maybe the integrated heat meter is also rubbish. But it can't be completely wrong, since I have an energy meter and can roughly estimate how high the power consumption of the heat pump is. If you work with roughly 1.3 kW at 6 kW heating capacity of the heat pump, that corresponds to a factor of 4.6. But that would be a heating cycle; the hot water is less efficient and drags the average down accordingly.
The COP bothers me a bit. On the other hand, heating costs are so low (2400 kWh per year, with heat pump tariff about €480 p.a.) that any optimization attempts are actually pointless. A COP of e.g. 4.8 would then correspond to an electricity consumption of 2100 kWh per year, or about €60 savings. That would be nice in the magic triangle between consumption costs, purchase costs/wear, and comfort, but probably negligible.

Heat pumps are maintenance-free. Or do you maintain your refrigerator. :)

The drilling costs, like all construction costs, depend on the region and the local price structure.
Furthermore, it depends on the type of ground and the required depth (we have 1x120m).
So there is a huge location factor.

But we also had offers like "brine heat pump €15,000 surcharge". How that comes about was also easy to explain, because the mentioned offer was not even based on a heating load calculation, let alone a valid calculation of the required drilling. It was offered by a plumber "from a single source," but drilling would have been done by a subcontractor from somewhere else, who was not involved in the offer preparation. So everything was just guesswork and with a large risk surcharge.
Since we built with an architect, it was no problem at all to have the heating system properly sized, to then approach the drilling company with the correct heat pump model and its capacity, to request a drilling with a known extraction performance. And then, oh wonder, very different prices come out.