700 seems a bit steep for a used set. 600 would be iffy, unless you knew first hand how they were handled for a year, or got to try the car and check for leaks.
Seems strange to change them for Bilsteins, as at least I found good coilovers are actually more comfortable on the road, in addition to being trackworthy.
I thought GAZ Gold was comparable to AVO GTZ which I had, so it should just be a matter of setting the stiffness, unless there's something wrong.
Well, hopefully not directly comparable, as AVO's lost the silly plastic lock-screws and started leaking in about 6 months of use...