Since the DFW Barbershop closed, XpresSpa in Terminals A and D is the primary option for hair cuts.
We've had a few other beauty places come and go that offer some hair services but not just cuts, to my knowledge. And XpresSpa does start their pricing at $30. I think it's fairly common for luxury travelers to go get a cut, a massage, shop at the Duty Free, then hit up some quail or duck with white wine at the Whitetail Bistro in D during layovers. It seems positively pleasant, seeing them float by with their bag of chocolates and bottles of wine, leaving the salon and taking a menu at the entrance to the bistro.