Top of the head...don't shoot me and prices have been all over the place.... £12.5-13k private, dealer would try to move it at £1.5-2k above that?
Only downside I can see is the mileage, over 20k per annum is a touch on the high side.
Have you been offerred the usual slap in the face from the stealer who would maybe say £10.5-11k trade in?