You are probably seeing a display bug and you will probably be charged the correct price.

That being said, if you *try* ticketing online, and you see the right price on the "complete your purchase" screen, it *might* work. More likely the system will reject the price as incorrect and either it will never ticket or it will ticket after 8 hours and you'll be mysteriously charged the correct amount.

If it does work and if UA issues you tickets for all passengers at a particular price, they probably won't come after you for more money later.