$400 is a good price. I paid $425 for mine and it is in excellent condition. Box, papers and extra mag all add to value. I have owned two of them. To appreciate the pistol you have to understand why it was made. Back in the 60's Germany was looking at the probability of millions of Soviets pouring through the Fulda Gap. Part of any resistance would require an armed citizenry. So, a dead-bang reliable and simple to operate pistol was designed, the "Volkspistole". It was the first production polymer framed gun. With a straight blowback design and 9mm Luger caliber a heavy slide and deep rifling to vent some gas was necessary. It worked and worked well. There was the VP70M with the stock and tri-burst feature and the VP70Z (Zivilian/Civilian) without. When the VP70Z was imported to the US the cutouts for the stock were filled in, nd you can still see the vestigial outlines of the cutouts on the frame.
All in all the gun accomplishes exactly what HK sought to do. Criticisms of the gun, while accurate, are usually made without consideration of the original purpose of the gun. The stock trigger is horrible but that isn't at all uncommon for this type of weapon where there is an auto/semi-auto function. The good news is that the trigger can be easily improved dramatically with a Wolff's replacement striker spring. It makes all of the difference in the world but it still won't be a great trigger pull. But, it will make for a very functional trigger where with a little work one can achieve more than acceptable combat accuracy with 100% reliability, again, what the gun was designed for.
Besides being very unusual and 100% reliable (and holds 18+1 rounds) the gun is an interesting peice of history in being the first polymer framed production pistol, and, being an fascinating example of the Cold War preparing to go hot.
BTW, once you have the trigger lightened it's a fun gun to shoot. Also, I suspect that the gun had the deep rifling (to let some gas escape) and strong striker spring to deal with hard primers and hotter 9mm subgun ammo that would have been encountered had the SHTF. I also suspect that the polymer frame was at least in part a weight-saving innovation to counter the heavy slide made necessary by virtue of it being a 9mm blowback design.