Difference in purchase cost between gas pump or heat pump

We are planning a new building. Ground area of the house: 10 x 14.5 m. Downstairs: 2-person retired household. Upstairs an apartment for 1 person.

Heating options/power supply:
a) normal gas boiler
b) geothermal/heat pump, electricity for it from the grid
c) geothermal/heat pump, electricity for it from own photovoltaic system and possibly electricity storage
d) geothermal/heat pump, electricity for it from own photovoltaic system, electricity storage and possibly [Cloud]

So far we have no information about how big the price difference is between purchasing a normal gas boiler and a heat pump with geothermal supply.
2 construction companies said a normal inexpensive gas heating would be sufficient because houses today are so well insulated, heating demand would not be that high. But is that future-proof?
And if heat pump, then preferably power supply from own photovoltaic system? With or without storage? Additionally [Cloud] solution?

My opinion on this:

Heat pump instead of gas, because gas is not future-proof, as you already say, even if it is initially cheaper.

Mentally decouple photovoltaic from everything else.
Make photovoltaic as large as possible, without storage.
Then the system will earn money for you for the next 20 years and even longer afterwards. At least if you manage to build it before the 52 gigawatt cap.
If not, it depends on the future political direction.

If at least the shell is not yet standing, nothing will happen before the 52GW cap.

We have an air-water heat pump and it cost us an additional €10,000 compared to gas/solar.

I can’t quite understand that. Where does the high extra charge come from? Was it a gas boiler from a “cheap provider” compared to a heat pump from a “premium provider”? Heat pumps cost more. Yes. And they also require a bit more effort for installation and commissioning. But if it ends up being such a big difference, you were probably ripped off. And what should also be considered is the elimination of the gas connection and chimney connection, both of which are not needed thanks to the heat pump. That should definitely be factored in as well.

But if there's such a difference, you were ripped off

It is an IDM A3-11. I would already count that among the better air-to-water heat pumps. Since we build turnkey and rather looked at the overall price/performance ratio, we would not say that we were ripped off. Incidentally, the differences between gas/solar and air-to-water heat pumps in the pool of offers were always between €6000-€10000. Therefore, your statement is exaggerated or you are simply misinformed.

Since a fireplace and solar are necessary for gas, the difference will no longer be significant.