There are three airlines offering flights to Chicago. The most direct route isn’t necessarily the cheapest – being flexible is key to finding the lowest airfare rates. For example, try searching by month to see the best time of the week to fly. The cheapest date is currently 23 / Nov / 2019.
You can use the filters on your search to see more flights and find cheaper rates – Chicago has more than one airport. So if you don't need to fly into Chicago Midway Airport, it's worth checking your other options. The 5910 km flight usually takes about 15 hrs 35 mins.
During this peak season, accommodation prices often increase too, so it's best to book early. Or you could keep your fingers crossed and hold out for a last-minute deal.