I just bought a Model 1 sales upper, M4gery, and I got the entire kit, including, charging handle, bolt, and complete lower parts kit, stocks and all, for $439. Great deal. Light and pretty cleanly built.
Now, it shot like shit at first, but then after a break in period and frequent cleaning, I found that it liked the Hornady V-Max and Barnes X bullets, and now it is stating to group around 1 MOA at 100 yds.
I think I did well, despite this being a "get my feet wet" upper.
Next 6.8 is likely to be a Noveske, L / W, or Model 1 fluted 18 inch SPR, with free-float tubes, rails, and thus, a little higher velocity from the 6.8 mm round. Really need to get it up around 2700-2800 FPS for game -killing velocity.
Model 1 : inexpensive
Noveske: better be a bachelor...
Hope this helps