My car so far, has cost Ł7,000 in OEM RS4 parts, Ł2,100 in wheels and tyres, Ł420 in suspension, Ł400 S8 Brembo calipers, Ł3,000 in bodywork labour / paint.
But realistically, I won't get anywhere near that amount if I ever wanted to sell her. I've also just purchased an S8 4.2 V8 motor for Ł900 delivered, yet to fit.
The best I can advise with a modified car, is to enjoy her, drive her till the wheels fall off. Not very likely with an Audi, or find someone in the narrow market your car appeals to, and then you're most likely to get close to what you want, in terms of price.