Have looked at used RS6's, M3's and the Scirocco.
....There was a superb RS6 Avant for sale via APS at Castle Combe this summer. I think it was an 03 plate, 75k miles, but religiously maintained and with literally £40k spent on full Sportec mods. Extremely quick and all for £30k.
There are some excellent value M3's around but you'd have to spend a lot on modifying a Scirocco to make it at all exciting imo.
Whether you tinker or renew, cars will always cost you money but it's the joy of driving them which is more important imo.