IMHO
From what it seems.... (if you are only wanting an M48 and not a real WW2 German Mauser),
you are only paying the extra money to have all the detail work done for you, ie cleaning, nice stock finish, etc.
I bought a real WW2 German Mauser recently from Classic Arms that arrived in less-than-desirable condition. But with a LOT of TLC, it is now something to look at. The second coat of Tung-oil finish is drying right now.
But $499 is a lot of money for an M48, and I feel that I've gotten to know this rifle better by doing all that detailing myself.