I just got very good prices to move up cabins for my trip next month.
I'm not sure how other airlines' apps and upgrades work, as I'm loyal to/stuck with American. They often offer discounted upgrades in the phone apps that are not available anywhere else. The offers can vary from nearly market-rate to screaming deals. (Note that on AA, the upgrades are by segment, not whole itinerary, and only offered for flights on AA's planes. And they don't earn extra miles—you're stuck with the miles/points you'd have earned on the original ticket.)