Bear in mind that the car you are interested in was made from 1989 all the way up to 2000, so a fresh import could be only 4 -5 years old and still on its depresciation cylce. Most older Z32s have reached the bottom of their depreciation and price will depend more on condition and equipment options or, indeed, level and quality of modification. As such there is no "price guide". For an older example expect to pay up to £6000 for the best and as little as £1500 for the worst. Young examples will command up to £10,000 or maybe more. There are few guidelines as, due to the pressures of SVA testing on cars less than ten years old, the importers don't seem to be bothering much with the Z32.
If you wanted to take a trade risk, I recently had some data from the Liverpool Port Auctions which tabulates average sale prices for a variety of models, e.g.
1996 SWB manual NA £4200
1993 2+2 TT auto £3000
1990 2+2 TT auto from £2250 - £2600
These are trade auction prices straight off the boat without MOT, SVA, registration, plates etc. and "as seen". You would have about two hours to assess the cars on offer before bidding. Obviously the same cars prepared for sale would command significantly higher prices, but it might indicate that there are no bargains in the Z32 market. If a private individual is selling a car "cheap" there is likely to be a very good (and potentially expensive) reason.