Looks like you could pull it off (as part of a France trip) for anywhere from about $200 for the worst seats on Sunday on up to $4,000 to go deluxe for three days. I've been pondering a retirement present of a trip to Lyon anyway, so I might just figure out how to work that trip around a GP weekend and make the trip to Nice for the weekend. My wife can visit Nice, and I can catch the train into Monaco for the GP each day.
Or I could just buy more cards
