Chuck up a brass round-head screw in your hand drill. Apply an abrasive paste and work on that bore. Cost? Pennies.
Tip courtesy of Brownell's Gunsmith Kinks books.
My grandfather recrowned a Type 99 Arisaka with that method (except he had solid brass balls that he chucked directly in his drill press).
It worked amazingly well. ...and they're self-centering.
(so long as your screw has no run-out, and/or the ball is actually round)