Asking for a friend here who's torn a couple of ligaments in his ankle and is supposed to be flying in Y TLV-JFK in a few days time. He's supposed to be keeping his leg raised as much as possible so that length of time in Y probably isn't best.

Apparently speaking to his travel agent, an upgrade to C would be around $1000. What are odds of being able to upgrade at the gate, check in or some other way and what are likely to be the costs?