ᐅ Assessment of Quotation Price for Insulation Under the Slab/Foundation

Hello,
we have received two quotes for a shell construction. Both include insulation beneath the ground slab.
The first is 6cm (2.4 inches) WLG038 for €9000 and the other is 10cm (4 inches) WLG036 for €2700. The prices vary quite a lot. What would be a realistic price for 105sqm (1,130 sqft)?

From my experience, I can tell you that the material costs are around 1000€.

With two people, you can install it yourself on a Saturday morning and then assist the masons a bit when installing the formwork for the foundation slab.

That was at least the arrangement I had.

Yes, more like 3000. The other figure is definitely much too high.

There is hardly anything you can’t do yourself more easily.
For that, I wouldn’t want to pay anything except for the materials, of course.
They just lay a few panels side by side, that’s it.

They probably made a miscalculation!?

Putting aside the fact that 9000€ is absolutely outrageous, I wonder what exactly was offered here. Why does one offer 6cm (2.4 inches) and the other 10cm (4 inches)? As if the planned building heights were a matter of personal preference. Who is the planner here and what are they actually doing?