$151 Cheap United flights St. Louis (STL) to Sun Valley (SUN)

Finding cheap one-way United Airlines flights from STL to SUN from $151 on Expedia couldn't be easier --- just filter by "Price (lowest to highest)." Alternatively, check out our budget-friendly round-trip fares from $291 for your next exciting adventure.**These prices were available on Expedia within the past 7 days, for flights departing within the next year. Prices and availability are subject to change. Additional terms apply.

Begin your search one to three months ahead of your travel date to score cheap fares on United Airlines flights from Lambert-St. Louis Intl. Airport (STL) to Friedman Memorial Airport (SUN). You can save 25% by booking your domestic flight 34 to 86 days in advance compared to last-minute reservations made 6 to 12 days out. You could also reduce costs by buying your fare on a Sunday, as it's 6% cheaper on average than a Monday, the most expensive day to book.* Nail your timing, and you can enjoy significant savings on domestic flights.*Ideal booking window recommendation is based on average round-trip ticket prices for January through November for 2024. Best day of the week to book recommendation is based on average round-trip ticket prices for January through October 2024. All data sourced from ARC's global airline sales database.

To find the earliest departures from STL to SUN with United Airlines, sort your results by "Morning" and "Early Morning." Choosing an early flight usually means cancellations are less likely.**Most reliable time of the day recommendation is based on January through August 2024 flight status data sourced from OAG's global flight data platform.

Depart from STL to SUN with United Airlines and enjoy a host of benefits starting with a rewarding loyalty program. When you book through Expedia as a United Mileage Plus and One Key™ member, you can also earn OneKeyCash™* to use on select future travel purchases.*OneKeyCash™ disclaimer - OneKeyCash™ is not redeemable for cash and can only be used on Expedia, Hotels.com and Vrbo.