From which reg?
N to EASA
I think €3400 inc flights would be the correct number for a one-day DAR service. In the US I agree it is a lot cheaper, it’s probably 4x the cost here in Europe for the same service.
For anyone thinking of going to the N (C of A issue) or coming off the N (Export C of A issue) it is always worth remembering you have to be ready for the DAR. He applies for a time window from the FSDO/FAA to come to you. He has some leeway to extend that time, but if at the end of the time window you are not ready then he needs to issue a denial letter. Which you don’t want. Hence you get the checklist for the process and work strictly to that before the DAR visit. In many ways, it’s no different than going for a flight test with an examiner.