Urban travel frequently involves getting on an airplane. In St. Louis (where all of these examples were taken), you'll want to get a look at fares for Southwest Airlines. Frontier and America West might have some strongly competitive fares, too. Every big city has a few dominant budget carriers that serve at least one of the major airports. In Europe, look at
EuroFlights.info for a quick directory of budget carriers in nearly 400 cities. In North America, a quick
fare search on Kayak or some other search engine might not reveal budget carriers. It is best to check
last-minute airfare pages here at About.com Budget Travel.