Here in the US KBB lists a 2013 Z6 for about 5,500USD. Seems high but as the 2012 was the first year of the Z6(I think), I would think 4-4500 would be a better value...especially sense they have been obsolete for so long now parts will start to be hard to find....even here soon.
That being said the Z6 was a tough little SxS and many still have them and are still giving good service. If it's that good and that low on miles...it may well be worth it.