I spent about $23 an hour for Frontier Airlines' premium class. I'd upgrade again, but only on one kind of flight.

Source: Business Insider

Ultimately, upgrading to Frontier's UpFront Plus worked out for me on this flight. Ash JurbergI paid $159 for Frontier's Business Bundle, which included an upgrade to UpFront Plus. The upgrade didn't come with much, and my seat was fixed in a slightly reclined position.