In the custom world, you NEVER come close to recouping your investment. I have thought about this exact project, but the numbers I crunched put me off. I did figure out that in many cases, you can buy someone else's custom for a fraction of what it would cost to build, so if you want a nice rifle to use I recommend that route. If you want an investment, you're going the wrong direction.
That being said, of the two, I think the 9.3x62 is a more fitting choice for a Mauser 98. That combination was made for each other.
