For liability you could require a fairly high lane fee, use of only your ammo to ensure no one uses anything that would cause accelerated wear or fires. By the time you get fees and ammo your looking at charging folks about $30-50, but you would have costs in power , moving it, wear and tear, wholesale supply cost for ammo, safety glasses, hearing protection. You may only net about $10 per customer.
Might be worth talking to a gun show promotion company in your area and see if they would subsidize your coming out there, or if vendors wanted to use coupons or some such thing so people could pay a fee to try a gun before they buy. Could help sell some guns. Other than that I'm not sure how you'd drum up enough business.