I did something similar for a few yrs about 18 yrs ago. Although, I did not move in the property, I took in work. I stopped by the gunshop and picked up my work. I quoted it and had a standard price for most common stuff. Set your prices, stick to them, and don't count their money. Just because you may be charging $25 labor to install a pad and they charge $60, don't start thinking about raising your prices after you learn what they charge. Set your prices up front based on local economy, and the local clientel with room for the retailer to make a fair profit. I was doing work for common folks on common guns like 870's, Mossbergs, Win 12s on occasion, and rarely any double. Much of my work was handgun repair and the occasional rifle work.
It was not uncommon for my retailer to charge 100% markup on my work. I knew that and was still good with it, knowing that the charges I established were making me good money. If you want all of the profits, you need to 'go it alone'. Even then, a gunsmithing only biz will commonly deeply discount charges for other retailers that provide a steady stream of work.
I would be very careful about moving in any equipment and tools you can't afford to loose, without a written sublease agreement. If these guys default on their lease or loans and get locked out, you're left without any legal standing to recover your stuff.
Probably your best resource here will be SKB (Steve Bertram)as he was in a similar arrangement a year or so ago.
