last year I wasn't able to find someone, who is officially hiring boats, but near St Geran Hotel near Belle Mare there were some small (private) boats anchoring.
I simply asked someone living there, who owned one. After a nice conversation he gave me his boat for 2 days, he was OK with 100€ (about 145USD) and a refuel, which was pretty much fair.
I have a german offshore-licence for sail- and motorboats.
btw: if you find someone officially hiring boats let me know...