Booking your journey from Chengdu Shuangliu Intl. Airport to Sea-Tac Airport at the last minute could help you save if you get lucky and find a bargain. However, tickets usually don't get cheaper closer to the departure date. If you wait around, flights could also be sold out or the best seats gone (because no one wants the middle seat). If you want to be on the safe side, book well in advance of the date you want to leave. Remember that some of the most awesome deals can be found up to 12 months in advance. If your preferred airline hasn't released its fares yet, check back regularly as deals are updated on Expedia all the time.