ᐅ Costs for Earthworks

My architect informed me today about the cost estimate for the earthworks (installation of ground collectors), and I’m quite shocked. Excavating an area of 400 sqm (4,300 sq ft) and then backfilling the pit is supposed to cost me 7,000 euros?! The soil on site is classified as type 4, and about 600 cubic meters (780 cubic yards) of soil need to be moved. I will install the collectors myself; this is only about the earthworks. Is this price normal? It seems very high to me...

Excavation work is relatively expensive when the ground is difficult to work with (hard to loosen, heavy in weight); soil class 4 would be moderately easy-to-work soil types, mixtures of sand, gravel, silt, and clay. Are there comparative quotes? (there should be; if not, obtain some).