I have a WWII era K98 that my grandfather picked up along the way and left to me. He had some work done to it (including a very heavy monte carlo stock, which I may replace someday, as it really makes it a pig to carry around -- but I've primarily used it for white tails, stand hunting, sot he extra weight hasn't been a huge issue). I love the gun, and good luck with yours.
I had it drilled and tapped, and a scope installed, back in the 1980s. Granted this was 25+ years ago, but it didn't cost anywhere near that much, and, even figuring in inflation, $400 to mount a scope seems really high.