The indoor range that I use has 3 rooms with 8, 8 and 10 positions in the rooms.
The range was built by a friend that that I used to work part time for. He sold the store 3 years ago. The man that owns it now last year replaced the air filtration system for the range. $17,000.
If you don’t have a gun store attached, I really don’t see how you can make money. The first thing I would do is check with a good reputable insurance company and get the price for liability insurance, once you find out how much that alone will cost, you might not consider it a great idea.
Personally I wish you luck, I do know that he makes good money on the range in the winter time but the summer slows down.
Recently his business has plummeted, the reason is that he made a change due to insurance (he says) he only allows factory ammo, no reloads.