I bought 4 of these back in October from groupon, they're expiring next week. They were $19 each when I got them, but given the short timespan I'm wililng to let them go for $15 each. The groupon is good for 20 minutes of racing which is normally a $40 value.
In terms of transactions I'll probably print out the groupons and also allow the purchaser to call f440 on the day of the transaction to verify that the groupons have not been used yet.
http://www.groupon.com/deals/f440-racing-challenge-ltd