Originally Posted by
LoganFlyer
Not really. Sioux Falls is on the other side of the state from Rapid City. So that'd sort of be like saying air fares are expensive to PIT because of a convention happening in Philadelphia.
There are certainly plenty of events in Rapid City and the Black Hills all summer, though. The OP seemed to just baselessly assume no one would ever want to go to that part of the country in it's peak season as opposed to South America in it's off-peak season.
The OP didn't provide particular dates but if flights to South America were under $300, it just as likely reflects low demand for those flights.