Yarlsberg

Hi, just signed up as am currently in the process of buying a 57 2008 350z GT roadster, ex company car , UK car, 1 owner with 15k on clock. serviced at 10k mid 09 , gunmetal with azelan and satnav. Can anyone offer up indications of what they think a fair private price I should pay for this- parkers says 19500-20000- I was planning on offering 18500. are these particularly in demand as i thought the price is quite high bearing in mind the new 370z is out shortly