For either the 450 or the 500 conversion you are looking at a new barrel, rental on a reamer and around $100 labor, not more then $150.
I do not have the reamer but rental is around 55.00. Barrels are available from the Montania Rifleman or Shilen and if you are intrested I will check on price and give you a total for the conversion, it will be on the "high side" that way you will have no rude suprises, the actual job should come in lower.