Unfortunately, modified cars DO lose a fair bit of money, come resale time. Modified cars tend to appeal to a narrower audience. Regardless of how much you've spent on it. My car so far, has cost £7,000 in OEM RS4 parts, £2,100 in wheels and tyres, £420 in suspension, £400 S8 Brembo calipers, £3,000 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 £900 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. Good luck!