I had a 45' Hatteras ("The Hooker") for several years; probably the dumbest thing I've ever done, but I'd do it again. I paid $70k for it in 1996 and had it chartered out in Grand Isle and then Fourchon. Had a captain and deckhand that ran the boat and someone to book the trips; trying to break even and get the boat to pay for itself, but that didn't quite happen. Sold it in 2000 or so.
Boat took on water one day and the engine compartment got flooded. Engines were good, but generator, starters, alternators, and much of the wiring had to be replaced. Boat had a pair of 6-71s and starters and alternators aren't cheap. I would figure on replacing just about anything that carries an electrical current if it got wet. You don't want to risk having something short out in the engine compartment, especially with gas engines. If the generator got wet, you'll need a new one; see if you can find a good used one.
I was paying several hundred a month for a slip, I think, but I forget exactly how much. Maintenance was another issue - I was charging $1,000/trip, and after you took out fuel cost, captain and deckhand pay, the rest was eaten up by maintenance. Boat was a 1971 model, I think, so it's age contributed to that.
A few more thoughts - "freak accidents" seem to happen quite often, so be prepared. I can remember running up the Mississippi one night headed to Venice, against the current, no steering (was steering with the throttles), no lights, and one transmission about to go (that would have killed ability to steer with the throttles), dodging cruise ships and crewboats, etc. Definitely a white knuckle ride.
Also, a boat that works perfectly well when moored after a trip will develop several problems while sitting at the dock.
Ok, I guess that's my $.02. Bottom line is that it doesn't sound like a bad deal, but be prepared.
66 Fairlane GT Convt, built 428 with E-brock heads, Toploader 4 sp
68 GTO convt., 455, TH400
70 RAIV GTO, 400, M21, 4.33
71 Javelin road race project, 401, T10