Double garage with basement or double garage stacked one above the other?

Dear forum,

we are building a prefabricated house and have also planned a double garage. Since we are building on a slope, we had a considerable additional cost of about €10,000 for the foundation of the double garage. In the south, a strip foundation is planned, in the north an L-shaped heavy-duty foundation, and in the middle a point foundation. On the east side, towards the neighbor, we have to close the side, and in the west at least halfway as well.
Therefore, the question arose whether we should basement everything.
The prefabricated house provider made us a proposal, namely
to basically put another double garage under the garage, which is called a multipurpose room.
The costs for this including the foundation amount to €37,000.

Now we are considering whether to completely remove the garage and commission a garage ourselves. How much money would one currently have to plan for a comparable double garage, for example from Ott or Zapf...?
We have a Neva double garage from Ott (see below) included in the house construction contract:

Does anyone have experience?
Or experience regarding a basement and a cost estimate?

Best regards

we are building a prefabricated house and have also planned a double garage. Since we are building on a slope, we had a substantial additional cost of about €10,000 for the foundation of the double garage. A strip foundation is planned on the south side, an L-shaped heavy-duty foundation on the north side, and a point foundation in the middle. We have to close the side towards the neighbor in the east and at least half on the west side. Therefore, the question arose whether we should basement everything. The prefabricated house provider made us a proposal, namely to basically put another double garage under the garage, which is called a multipurpose room.

Such individual questions are almost impossible to answer without knowledge of the house and especially the plot. If I understand correctly, the house manufacturer wants to basically wall up the foundation with side walls and build a floor, which sounds like a nice botch to me. Under a prefabricated double garage, I would not have planned anything other than another prefabricated double garage from the outset. In such application cases, the "let’s see" planning method avenges itself appropriately expensively ;-) I can well imagine that the prefab garage provider will quote a new price under the changed conditions, which you will hardly believe (or even, if you don’t tell him anything about it, won’t even unload the things). Why visit such a forum at all, if you only ask individual little questions, even though you have a slope property? You could probably have saved high five figures just by the simple "trick" of discussing your project holistically here!