And Sun Country Airlines, which flies 737s from Minneapolis/St. Paul, where it is based, to more than 30 destinations throughout the United States, Mexico and the Caribbean, will begin flying to London Gatwick on May 27 with rates from $422 one way in the summer.

Never heard of these airlines? That may be because of their low-profile business style, which typically focuses on linking small cities to vacation destinations, largely avoiding direct competition with bigger airlines, and relying more on word of mouth than costly marketing blitzes. Some, including Direct Air and Allegiant Air, in Las Vegas, even refuse to pay to list fares at online agencies like Expedia or Travelocity, which means that travelers have to visit the carriers’ own Web sites to find their flights.

All of this helps keep costs down and fares low. “We don’t have a massive overhead like we would if we were a legacy carrier,” said David Meers, chief operating officer at Vision Airlines. In addition, the budget carriers’ low-fare strategies involve selling not just airline seats, but also hotel rooms and car rentals. With packages, Mr. Meers explained, “there’s a little bit of a margin for the airline as well, which helps to defray increases in fuel prices.”

One of the tradeoffs of flying a budget carrier used to be having to pay fees for things like checked bags and snacks, but now that most major airlines charge for the same things, such fees are almost expected. Allegiant, for example, charges for drinks and snacks, checked bags and seat assignments. Vision, on the other hand, offers free drinks, snacks and seating assignments.

Another issue to be aware of is the age of the planes. Some of the budget carrier planes are on the older side. Allegiant, for example, flies MD-88s, which are, on average, 21.5 years old. Vision’s fleet, as well as aircraft chartered by Direct Air, include some older-model Boeing 737s (which were not subject to airworthiness inspections in the wake of the recent depressurization incident on a Southwest Airlines Boeing 737-300 series aircraft on April 1). Each carrier is subject to the same safety and maintenance regulations as their larger counterparts.