If your spending the money to have the action "trued" I can't believe getting the same smith to chamber a barrel would be much more? As far as the specs, not my cup of tea, but if your question is how much you will save by going the barrel nut route, I don't think it will be much if your spending the money to have the action trued up.
Ps.... I'd also imagine there would be some extra inletting /stock work since Remington's aren't set up for the nut.
