I'm a USAir flyer (since I'm based in PHL) but I have some travel coming up this year to PVG, which will likely be on UA and have a question - hope this is the right place.

Here goes - my company will only pay for a discounted Y ticket, but I'm hoping to fly home at least in J on the PVG-west coase (likely SFO) portion of the flight.

What are my chances of getting offered a buy-up from Y to J at check in for this route?

If one was offered, what is the typical price range?

Thanks!