Pretty Easy to do yourself, make sure you gave good Batteries and Battery Connections are Clean and have a Good Ground at the Block just follow the cable from the Battery to where it connects , also check the wires on the Starter see if loose or dirty connections,
that engine the Starter is mounted top rear and very easy to get at .
if that does not the starter can be rebuilt in Toledo or you can buy a new one on Line pretty Reasonable , easy to install..
I am docked at Meinke West and out there often live 15 Min away if want me to look at no charge message me , Been around Boats and complete my own repairs for 60 years .
this time of year all the shops will be busy and you will pay big bucks, I do not want to take work away from them but with price of gas going up have to save somehow ...