I understand that the OP asked what marinas were charging but many of us prefer to do our own work and save a considerable amount of money.
If you have the opportunity and the place to clean your boat after it comes out of the water the sooner it is done the easier the job is. Slimy Grimy was recommended above and that product does work well. I have put it in a small pesticide pump can with hot water and by the time you walk around the boat spraying the hull, the stain is already running off where you started.
What I can do in an hour will save $250 - $300. That is an hourly rate that I am happy to work for!
It is available at Amazon for $24.95 and one container will last you more than one season (unless you are cleaning the Mount Washington)
https://www.amazon.com/Slimy-Grimy-G...y+boat+cleaner