Doesn't your "friend" have even a remote idea of what he needs?
Have you been friends very long?
30K for an overhaul? Not even close.
If you took care of fuel and insurance and paid 300 euros per hour, you would get a very cheap rate and he might just about break even.
I particulaly like your comment that he will have to pay the complete replacement cost when the time comes, if you "rent" it or not.
I guess that's what friends are for.