Costs for earthworks

My architect informed me today about the cost framework for the excavation work (installation of earth collectors), and I am quite shocked. Excavating an area of 400 sqm and then refilling the pit is supposed to cost me 7000 euros?! On site, the soil is class 4, about 600 cubic meters of earth need to be moved. I will install the collectors myself, it’s only about the excavation work. Is the price normal? It seems very high to me...

Earthworks are relatively expensive when the ground is difficult (hard to loosen, heavy); soil class 4 would be moderately easy to loosen soil types, mixtures of sand, gravel, silt, and clay. Are there comparison offers? (there should be, if not, obtain them).