There are two airlines offering flights to Sapporo. 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 14 / Mar / 2019.
You can use the filters on your search to see more flights and find cheaper rates – Sapporo has more than one airport. So if you don't need to fly into New Sapporo International Airport, it's worth checking your other options. The 8724 km flight usually takes about 22 hrs 25 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.