Mausers are great actions, but (depending on what your gunsmith charges), by the time he's done modernizing a mauser you could have the cost of a new or used modern action.
I.E...Drill & tap, replace the bolt handle, new trigger, machine off the stripper clip for scope mounts, convert the old safety, machine the trigger guard...etc. You may not do all of those things. If you really want a rifle off a mauser, i'd talk to your 'smith and see what he likes to do to them.