No semi is worth that price in my opinion. Thats why I no longer own it.
I know the feeling (I own a Five-seveN and am mighty tempted to sell, these days). I ended up getting the kit I was looking at for 650$. That's a lot for some scrap metal
but the existence of both repair sections and replacement barrels allows for completing the rifle, which would then be worth a pretty penny (even as a reweld) if I ever feel the need to sell to make more room in the future.
I checked out a video on the construction/internals on the gun at forgottenweapons.com and it is ridiculous
how over-thought and over-designed these guns are. The locking rollers (or levers, rather) have about 1/3 more bearing surface than a G3, and the bearing surfaces on the bolt are brazed-on superhard steel inserts. The bolt itself is far more massive than the G3's. According to the video, the G3 was originally designed for an intermediate round, and is only marginally capable of handling the more powerful 308. The Stgw57 was designed around the 7.5x55 from the start, and is therefore more massive, but better suited to round's power ("better" being subjective, I'm sure
The barrels available are 7.62x51, but rechambering seems possible (if not practical, due to caliber scarcity, fluting, and a funky shoulder contour) for a more "accurate" reproduction. A daunting build, indeed