RE: Cracked transom, 1993 Pro-V 1775
It looks like a rotten transom core is what caused the failure. The core is what gives the transom is strength. The aluminum on the outside of the transom is merely it's skin. The same thing that happened to your boat, happens on glass boats all the time. Only repair on a glass boat is ussually alot bigger project. The cuplrit in your case is most likely an improperly sealed motor mounting bolt or thru hull fitting.
You need to remove the motor, remove the transom cap, take out the old transom core (what's left of it), have the damaged aluminum repaired (welded), replace the transom core, and re-install the motor.
Even if you were thinking about buying a new boat, your going to have a hard time selling that boat with it needing a new transom.