Dood probably hooked the battery up backwards and smoked the alternator. Ready for a project? Gonna be tough to truly diagnose before you decide to purchase, so it's kinda a crap shoot. It's possible that it's a good deal.
If it just needs a new battery and alternator, it's a steal. You'd want to check the wiring near both, and attached to boath. Motor should still start with a different battery. Battery could have frozen too, but strange he walked out to see it smokin.
No idea if they made that size or not. Google it. Still think you should get your tale moving and check things out on that boat. If the starter justs clicks, tap the solenoid a couple times. If that doesn't do it tap the starter. Unless there was a fire, the rest of the boat shouldn't have been hurt. Probably just battery, maybe starter, solenoid, or alternator.