The Frontier dealio from STL to MBJ might not be what it seems. I think that Apple, which wholly owns usa3000, is chartering its STL/MBJ sat/sat trips using Frontier. I don't think these flights are going to be bookable on Frontier, only Apple. At least they are not in the system as of this moment. Rather than reducing costs from STL, I think this move may have the opposite effect. Those days of $99 last minute flights seem to be over.
And, it looks like Funjet just dumped Vision Air as its charter carrier in favor of Sun Country on its STL/MBJ route.
The best scheduled air seems to be USScare via Texas on an early am flight, almost always less than $500....