You might want to call Mitchells and ask what those 308 Tankers are made from. Ask about the barrel and where it came from. How is the rifle as a shooter and not just a collectable? To change/convert a Mauser that was an original 8X57 to a 308win would cost more than $495 if you want to go with the 'carbine' style that Mitchells have. It's not a bad price for a rifle/carbine in that class depending on quality.

As Rudy stated, the CMP has rifles that will hold their value a bit more...but it's all in what it's worth to you.