Chazal bring down that the “payment’ to the Rav for negotiation and execution of the transactional documents to effectuate mechiras chometz with a goy should be consistent with what one would pay to any other professional for the services provided. Most good contract and transactional lawyer charge at least $500-$700 hour so that should be a good starting point. There is also a school of thought that the charge should be a fixed percentage of the value of the chometz being sold (sort of like the real estate broker’s commission on a property sale).
