I was tracking a Thursday night LAX-JFK red-eye last month, and I believe the price generally went up as the date approached. There’s some seasonality to it, but you could also try looking at the same flight, same day of the week, for the weeks between now and then.

Is that $800+ upgrade from the “My Trips” page, or is it the price difference between your current ticket and the lowest currently available D1 fare on that flight? I have a December flight that I think they were asking $800+ to upgrade, so I set an ExpertFlyer alert for Z-fare availability (~$600) and ended up just paying the difference (~$250) to upgrade.