They have access to a special inventory it seems, a friend of mine was booked on spirit Last week and spirit did what they do best and he was stuck in the airport without a flight he called amex platinum and the found him a c&p flight for 9000 points and $110 I didn't check the rate but I would assume it was more than that a half hour before it left
It as dtw-NYC but a 1/2 hour before departure is usually at least $300