If you can find a cheap airfare to, say, London, it's tempting to then want to switch over to Ryanair or Easyjet for the shorter (and significantly cheaper) hop to your actual European destination. Before you do that, I'd like to throw in a word of caution for the uninitiated and give you five simple tips for deciding if this is really worth your time and trouble.
1. Flights on European budget airlines are usually from secondary airports. In London most cheap flights are out of Gatwick or Stansted, where few international flights from the U.S. land. This means an expensive and time-consuming transfer that you should budget for. Sometimes these airports are really out of the way.
2. Flight schedules aren't conducive to connections. This means that flights are scheduled when it's cheapest to take off (usually in the early morning or evening), which will often preclude a transfer from an arriving international flight. You'll get to your final destination the next day and might also have to spend an extra night in your connecting European city on the way home as well. Budget for that.
3. Luggage is an issue. You'll have to pay to check your bag on virtually all the European budget carriers. You'll pay a lot extra if your bag is overweight (the limit is usually 45 pounds rather than 50 pounds). Carry-ons are strictly limited by size and weight, and you are almost always limited to 1 (not 1 plus a "personal item" or 1 plus a computer or 1 plus a shopping bag). There's no checking your bag through to your final destination; you'll have to collect everything and transfer it yourself.
4. Check-in times are strictly enforced. Generally, if you miss your connection, there's no putting you on the next available flight. You're just out of luck and will have to pay for a new ticket, often at a much greater price. (This policy, however, varies by airline.)
5. Nothing is included. On most of these airlines absolutely nothing is included in the fare except transportation: not water, not food, not a little headset, and if the owner of Ryanair gets his way not even the toilet. Now, this also varies by airline, so you do need to do your homework.
Of course, there are exceptions. Aegean Airlines, considered a budget carrier in Greece, not only offers excellent customer service but also allows free checked bags and sometimes serves meals.
Find out which European budget airlines flies to your destination at www.whichbudget.com.