In a couple weeks, I'm going to be flying on United to Chicago. On the website it says that you can purchase an upgrade to Economy plus at check-in, but it doesn't say how much it costs. The flight I'm looking at to upgrade is DEN-MDW and according to the seat map (which I know isn't the greatest indicator of how full a flight is) the whole back of the plane is full, and there is maybe 6 seats taken in the economy plus section. I don't really need the extra legroom on such a short flight but I'm curious to experience the difference because I'm trying to decide whether I want to fly United to China later this year, and if economy plus makes a big difference, then I would probably take United because I know I can get an upgrade then.
So anyways to make a long story short, how much is the upgrade to Economy Plus at check-in?