The economical way is owner with more time than money guided by a
knowledgable helper who has done it before.
A couple guys have done that in our shop.
UH

Forgive the obtuseness, but how long does it take to strip the gelcoat
off, say a 15 m wing?
I guess that would be the easy part, because then one needs to build
it back up and check the profile, yes? How long for that?

I'm probably not going to like the answer... I'm very glad that the
gelcoat on my mistress is in great shape.