I'm in the final stages of buying a boat, and the generator is not working.
The seller has agreed to fix the generator as part of the sale, or replace
it (up to a maximum, yet-to-be-determined price) if it's not repairable.

It currently has a Kohler 5kw gas generator.

What would be the replacement cost if:

a) I got the same unit as a replacement

or

b) I replaced it with a diesel generator (and had to add a small diesel fuel
tank)