I had one for a few years. Very accurate pistol given decent ammo...100yd. offhand hits on 8in. plates were np real trick on a good day (of course, I had eyes back then!
) The gun was reliable and HUGE! The barrel will get so hot after a magazine or two rapid fire that it will burn a hole in a vinyl truck seat...trust me on thet!
I would not pay a lot of money for one simply because I think they have been obsoleted by better handguns, not to mention that tryibng to get magazines or other parts is most likely a near impossibility. As a curiosity, or to someone who has an idea of what (if any) "collectors value" it may have maybe $500 is a fair price, but it is way more than I would be willing to pay for a range plinker. Others may feel differently, and, for sure, the pistol is not "junk", so at least it will not fall apart on you.
a link to a little info about the GB...
world.guns.ru/handguns/hg71-e.htm