One name to keep an eye on is Mark Sanchez, who seems likely to be released by the Jets before they have to pay him a $2 million roster bonus on March 25. Sanchez's numbers aren't any better than Christian Ponder's, but he has been to two AFC Championship Games (though admittedly with better defenses than Ponder's had). Sanchez is only 27, and if the Vikings aren't going to bring back Cassel, they might look in his direction before they consider some of the other names in this thin group of free agent QBs.
I expect the Jets to retain Sanchez beyond the start of the league year just in case there is enough interest in him to acquire value in a trade. In truth, that's probably a long shot, but the Jets have absolutely nothing to lose by keeping him on the roster (as you'll recall they did with Tim Tebow in similar circumstances this time last year). It's also not completely out of the question that the Jets would opt to try and retain Sanchez on a restructured deal as Kristian Dyer speculated last week. Keeping him under contract enables them to control his rights and who he is permitted to negotiate with.
There's a two week gap between the beginning of the league year and the due date for Sanchez's unlikely-to-be-paid roster bonus. If most of the best backup quarterbacks on the open market are being picked up during that two week window, then perhaps you could end up with a situation where there is more than one team interested in signing him and entice one of them to give something up to secure his services. The acquiring team could renegotiate his contract, none of which is guaranteed, as part of the transaction.
Like I said, it's a long shot, but if the Vikings and a team like the Raiders (who have been linked with rumored Jets target Michael Vick) are unable to address that need in those first two weeks, perhaps they could be played off against one another. I wouldn't expect much in the way of compensation though - a low pick, an exchange of picks, a conditional pick or another player with warts would be about the best you could hope for.
It makes no material difference to the Jets' cap situation whether Sanchez is cut or traded, as long as that transaction happens before March 25. The only exception to that is that if he was released rather than traded they could, in theory, defer some of the dead money to 2015 by opting to treat the release as a post-June cut. I doubt that's a consideration, though, because they should have plenty of cap room in both years.