Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Sioux Falls to Oshkosh as you normally would.
For a flight from Sioux Falls to Oshkosh, you will be flying from Joe Foss Field. Sioux Falls Joe Foss Field (FSD) is just 2.6 mi from the center of the city. Joe Foss Field is the only Sioux Falls airport and it handles 0 outbound flights to Oshkosh per day. 3 airlines have flights to Oshkosh from Sioux Falls Joe Foss Field on a regular basis.