Ah, OK. I don't think they're RS6 wheels, you got me confused with your first comment. Specs are 20" x 9", ET37 so A6/A7 fitment.
I'd be happy to pay up to around £1,200 if they were immaculate, lower if they need any work. Without tyres.
With tyres, depends on the condition of the tyres, add another £400 tops?
If you can get them cheaper, all the better.