Welcome aboard and sorry to hear about the loss of your father.
What engine and drive is on the boat, 5.7 Alpha?
I recommend that you watch a u-tube or two on the job to determine if you think you can handle the job.
Not that hard IMO but a few special tools required. While doing the bellows I would also replace the gimbal bearing, water hose, trim and limit switch, and lower shift cable.
Since the boat has been sitting the impeller should be replaced, this includes changing the gear lube.
Tune up is like a car and change the oil. Oil has to be sucked up the dip stick tube after warming engine.
Hard to quote price as labor varies and I have no idea where you are but if you figure out material cost labor will be about equal so double for total cost.
1997 2400 SCR
5.7 Vortec / Bravo 2