Expensive plot + single-family house 155 sqm + cellar KFW40+, financeable?

Earthworks are budgeted at €3000. There is no more information. The soil survey has already been done. According to the construction service description: Construction electricity is included. Likewise, builder's insurance, "all construction equipment, building materials, and scaffolding will be provided by us for the duration of the contractually agreed services. This also includes construction electricity, construction water, and the fees incurred for these. The construction debris generated from the services we provide will be properly disposed of by us." For soil excavation, soil classes 3-5 are assumed. And further: "If your house is planned with a basement, the excavation pit will be dug, and the excavated soil will be stored on your property. (...) After the basement is built, the work areas will be backfilled up to the height of the existing terrain and compacted in layers."
Regarding the additional question: Everything including parquet up to €60/sqm in bedroom/guest room/office/living/dining rooms. Floor tiles in the remaining areas €40/sqm. Painting work: fleece wallpaper + white paint. Inner door e.g. €350 as a complete element (?). In the basement €210 per element.
All according to the construction service description.

We do KFW40+ more for ecological-ideal reasons than economic ones. Why do you see the financing as a problem?
We have already had informal talks with Dr. Klein, Sparkasse, Apobank, and Volksbank, who did not see the whole thing as so critical. To be fair, I have to admit that Interhyp also said it would be tight.

The blinds were an extra budget for a corner window on the ground floor, not for the basement. The basement is a pure "utility basement." Once a "play basement" for the children and once a sports basement for us (6 bicycles in the house, etc.) The doors from the hallway are equipped with "climate doors." Regarding the garden/outdoor facilities, I had already thought of something like that.

I haven’t had hope for cheap building for a long time... ;-) Although, as long as we buy the property first and then build later, I have hope that it won’t get more expensive then. :-)

"If your house is planned with a basement, the excavation pit is dug and the excavated soil is stored on your property. (...) After the basement is constructed, the working spaces are backfilled up to the height of the existing terrain and compacted in layers."

And what about the removal of material that is no longer needed?

This is not apparent from the construction service description. I need to inquire again. Otherwise, it is very favorable when compared with the experiences here.

And the removal of the material that is no longer needed?

On our property, only quantity X of the excavation Y could be stored. Z=Y-X had to be transported away. In total, I believe Z=16 wheel loaders. However, 4 had to return later for replenishment. "No more excavation material fit on the property," yeah, right....

That alone cost 5000€. And this is sand that does not have to be deposited, but can be reused as fill sand in other construction projects.

The basement seems cheap to me.

I don't find that unlikely now.
The bare standard basement cost us an extra 26k compared to the base slab.
Depending on the requirements, a bit of screed and surface-mounted electrical installation, that seems realistic to me.

Plus earthworks, of course.

I don't find that unreasonable now. The bare standard basement cost us an additional 26k compared to the floor slab. Depending on the requirements, a bit of screed and surface-mounted electrical installation, that seems realistic to me. Plus earthworks, of course.

I think that's super cheap. I've already heard of basement prices of 100k (in our area). I find that very expensive, but I would have estimated 70k. By the way, I believe you can build a house for that amount of money, but I doubt the mentioned wishes with that budget.