Ground not 100% load-bearing - Are additional costs for foundation sufficient?

Hello, we have a soil report for our property:


Since our soil is not 100% load-bearing, additional costs will arise for us here.

The following passage is already included in the general contractor’s standard:

Foundation
The foundation is carried out using a reinforced concrete slab 20 cm thick made of concrete C25/30 including a continuous frost skirt, which is constructed as a strip foundation approximately 30 cm wide and 90 cm deep after the topsoil has been removed by machine excavation using earth formwork.
Below the concrete slab, about 15 - 20 cm of existing topsoil is excavated between the surrounding foundations, stored at the side, and replaced by delivery and installation of a gravel cushion. The filling of the gravel cushion is done on an existing load-bearing subgrade with a minimum bearing capacity of 0.2 MN/m². A construction foil is laid between the concrete slab and the gravel base to prevent water loss when concreting the slab.
The scope of services includes 15 linear meters of KG pipe including the required bends and connecting elements as a base line under the concrete slab.
The base lines end about 50 cm outside the building structure.

We have received the following offer as an additional quote upon request:

Soil replacement/foundation cushion
Excavate existing soil up to 0.80 m depth or dig out, store excavated material at the side, deliver load-bearing infill material, and install it layer by layer in the existing excavation as a foundation cushion with 1 m overhang all around.
Within the soil replacement area, a continuous frost skirt made of concrete C25/30 will be constructed under the concrete slab, 30 cm wide and 80 cm deep.
Quantity of compactable material to be delivered approx. 320 t
Soil replacement area 15.50 m x 12.50 m
Additional cost: €6,830.00

Earth excavation disposal
Transportation and disposal of uncontaminated excavation material with a 3-axle vehicle including loading of the transport vehicles with an excavator
Quantity: 220 t
Additional cost: €2,618.00

So about €10,000 additional costs.
Is this sufficient?
We have been with various solid house providers and so far additional costs between €3,000 and €17,000 have been quoted.

So I am somewhat confused.

The transport is in my opinion not quite favorable, otherwise okay.

Perhaps I am under a misunderstanding, but with what material is the filling and compaction supposed to be done?

So far, I have only read "compactable material" with 320t. Concrete recycling material? Gravel?
Does the GU elaborate on this further here?

We will probably handle the removal of the soil ourselves. There is a landfill nearby. I just wanted to know for the calculation.

I think it is gravel. But it is not precisely specified. I will have to ask again.

Do it yourself? Drive with the trailer 150 times?

We will probably take care of transporting the soil ourselves. There is a landfill nearby.

I can't believe that. Do you have a 40-ton truck? With a normal car trailer, we wouldn't have made it 10 meters on the landfill before getting stuck.

As RobsonMKK wrote, you would then have to drive for days, because the cost of using the excavator for all the loading and transporting is so high that it no longer makes sense.