Watch Saving Salvage on YouTube and a few videos on his rebuilt engine on an R8. Dean Shaw knows his way around cars. The R8 is a supercar, so rear engine, and an absolute pain to access anything. Also expect the usual Audi prices for any replacement parts.
Also watch Ricky from REPerformance on YouTube. Again, very, very experienced with these cars.
There are 186 on sale on Autotrader ranging from £190k to £28k.
You can afford to shop around. You want a service history as long as your arm. A genuine car will have documented history, probably garaged, and the owner will be able to bore you to tears with every nut and bolt. That’s the kind you’re looking for. Also keep back cash reserve for unexpected bills.