So, doing the math... a quick look around the web for the Audi RS6 says 15mpg city/22 hwy. This is a road trip, so let's say something conservative like 18mpg. Let's even say they take the same route as the Tesla. Also, the RS6 takes Premium gas, which was $3.29/gal in Boston just this morning when I drove past a major gas station.

759 mi/(18 mi/gal) = 42.17 gal

42.17 gal*(3.29 USD/gal) = USD 138.74

That's still not a hell of a lot of money, especially if you're driving something that costs three orders of magnitude more.