John Dagys at Speed
had an article with lots of details on the Grand Am Audi.
Some interesting points from the article:
Nobody has bought one yet,
They are only making 4 (unless there is a larger than expected demand),
It costs $438,000 (which I assume is much more than a tuber Mazda, and for reference you can buy a DPG3 Riley for $405,000 with no engine),
You cant convert a GT3 to GA spec, but you can go the other way.