Do you have any pictures that show the full cave? That might help us get a sense of what it is worth. I didn't mean to be harsh on you, but it seemed to me you were completely pricing out potential customers. If the "cave" is a simple box like structure with vertical walls and a horizontal roof, like what is pictured on your site, you won't get many repeat visitors except maybe by little kids who need baby-sitting. If there is more to it, that we don't see, it might keep people's interest and they would be willing to pay.
I presume you have visited other, quality gyms in New England before you made your business plan and built it. In your first post, I got the impression that you built a little cave in your store to use your self and encourage interaction with the community, thereby getting more customers and building loyalty. If it is meant as a profit maker in itself, I think you have to be thinking of a more advanced structure.