Another domestic airline will charge passengers for carry-on bags. Denver-based Frontier Airlines announced Wednesday it would begin charging passengers who book tickets on third-party web sites -- such as Expedia and Orbitz -- for bringing their bags onboard the flight. Passengers who purchase tickets on Frontier's web site will incur no additional charge for a carry-on bag. The cost of a carry-on for passengers booking on third-party sites is $25 - $100.