It seems like a reasonable rate for a US resident, but your British mate can do better.

AutoEurope (first I checked) comes back as £315 inclusive, including insurance, taxes etc.

That's about $500 and he can get 8.5% Quidco cashback on top of that, bringing it down to $460 net. I've no idea how they would respond if one driver were on a US license and the other on a British licence.