There's also an Aston Martin Ringtaxi available (a green motorsport version of the V8 Vantage), or at least it was when I was at the Ring in August. One ride = 299 EUR if I remember correctly.
That's me and E92Fan (giving me good advice as he's a pro) about two months back, having a great time:
Alpina_B3_Lux
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Audi R8 LMX, BMW M550i xDrive (G30 LCI); gone: Alpina B3 3,3 (E46), BMW 335i, Audi R8 V10 manual, Audi R8 V10, BMW M235i, BMW 550i F10