So where are we at with 89 prices ?
Well how about a 105k 09 30i auto for £9k 8) very well specced with sport seats + nav although wheels look shot & don't work with the DSB imo
http://www.autotrader.co.uk/classified/advert/201607185950990?search-target=usedcars&make=bmw&model=z4&year-from=2009&minimum-badge-engine-size=2.2&postcode=bb120hr&searchcontext=default&radius=1501&page=1&sort=default&onesearchad=new%2Cnearlynew%2Cused&logcode=p&adPos=4
Now this 23i 90k example I can tell you has been for sale 3 months

on 19s with nav it was for sale at £11k when I was looking but se seats & the price ruled it out
http://www.autotrader.co.uk/classified/advert/201606275317120?search-target=usedcars&make=bmw&model=z4&year-from=2009&minimum-badge-engine-size=2.2&searchcontext=default&radius=1501&postcode=bb120hr&page=1&sort=default&onesearchad=new%2Cnearlynew%2Cused&logcode=p&adPos=5
& for those wanting less on the clock at 23i DSB 32k sport seats 2010 for £11750 ? on 17s doesn't help & I think its too much
http://www.autotrader.co.uk/classified/advert/201607145838760?search-target=usedcars&make=bmw&model=z4&year-from=2009&minimum-badge-engine-size=2.2&searchcontext=default&radius=1501&page=2&postcode=bb120hr&sort=default&onesearchad=new%2Cnearlynew%2Cused&logcode=p&adPos=9