Depends on motor I would imagine. Some take longer than others but I wiuld figure anywhere between $200 to $400 labor & you provide the reeds. If mechanic has to supply them he deserves SOME markup on price of reeds I'm sure. Just a guesstimate.
I agree. The bigger issue is finding a competent mechanic right now. The good ones are very busy, so try to schedule to bring the boat in when he's able to do the job, and have the necessary parts on hand or in stock to complete.