Im a sprayer at an Audi approved garage it would be around £2000 + VAT depending upon the condition of the bodywork.
You have to remember a huge chunk of that, around £700 goes on materials and as Glasurit are the only Audi approved paint it tends to be expensive stuff, but you get what you pay for.
All our paintwork comes with a 10 year warranty.
It worries me these garage who claim to do a respray for 600-700