If I were tasked, I'd call a half dozen larger AMCs, have them bid the project. My fee to broker it would be 1/2 of the total fee quote range between high and low bids.
Not enough information. Are they real estate, on rented pads in parks, etc.Why would someone pay half of the total fee quote to have you call six AMC's for bids?
If the results are not important, then his client can call the AMC by themself and the AMC will find the cheapest appraiser to do it to pocket as much of the fee as possible.
If it is important and they want someone else to handle it, then they can pay a fee to someone to find the best person for the job. Total cost will probably be $160k-$200k.