HI Quirks.
The GPX and ZZR250's are very similar bikes under the skin. Both have been in production for many many years and as a result there are heaps of spares for both models. The GPX and ZZR 250 had very little in changes over their life span so the year model would be less important than the km's and condition. Personally I think anything over $5K for a second hand one is a bit high. If you only plan to keep the bike for twelve months then I would look for something a bit cheaper so you don't lose out on resale.
Have you checked the for sale on this site?? There may be something there that may catch your eye from time to time.