Unfortunately, I don't think it would be quite so easy and inexpensive. The tanks are under the cabin sole and would have to be cut out to be removed along with removal of some of the floor and structural bracing.
Right you most certainly are... I was, as we all often do, thinking more specifically of our boat. Only 22 gallons, tank is easy to get to and remove. Had it priced out 3 years ago when we got the boat as we thought there might be an issue. We've got a great local shop in a competitive market that includes a lot of commercial marine so it's more reasonable than a lot of places. Speaking of PITA tankage to replace, the worst I've ever seen was helping a friend remove a fuel tank from a Norseman 447... It was a living hell and no way to get it out without removing much of the teak around the companionway hatch. I can't imagine that that one cost the owner less than 5-6k.