San Diego to Denver

We flagged this route at $113 just last week, and it's dropped again to $45 nonstop on Frontier, 82% below the usual $257 round trip. Dates are open over the next couple of months, and Denver is a great low-cost gateway to the Rockies for ski season or early hiking trips. This is one of the cheapest fares we've tracked on this route, so it's worth grabbing while the price holds.