:shock: Why would you want to convert a 25-06 to a .257 Roberts? You already have a better caliber, why not use it?
Now, depending on the brand of barrel you use, that could range from $150. (Adman and Bennet) to $500 dollars for a better (?) brand name. For a gunsmith to remove and replace, head space and re-blue, you can expect another $150-250. Depending on what you go with, you could have 5-6 hundred tied up in the conversion. Look around, you can find a replacement rifle for less.