Good price for an S6 Avant?

[Beau]

Hi there - only just found this forum. After many test drives I'm looking at an S6 Avant (much as I would love and RS6 budget doesn't allow).

2002 / 02 plate
55k miles
Silver / full black leather
No satnav
Immaculate condition IMHO

Independent Audi specialist is asking £20,995. How much lower should I try and go? No part-ex and cash waiting.

TIA
Beau