Would be interesting to see what the "minor" modification will be. Other than that, it looks like a sweet receiver. G3 mags are all over the place, even the 30 rounders.
Just off the top of my head, I'd probably say another 800 at least. About the same as a new gun. Hell even if it's a little more, at least it won't take 30 dollar mags...
The .22LR conversion looks sweet. It looks a lot like a Ceiner kit, but then you wouldn't have to deal with the douche that owns that company.
Too bad you can't have it shipped to MD due to 25 rnd mag sold with it... I might just have to have my Dad buy me one when I go visit home later this year...