Bikes are big. That one geometric fact means that airline companies are likely going to charge you extra.
How much extra depends on the airline. Fees range from Jet Blue and Southwest's reasonable $50 per bike each way to the $200 one-way fare US Airways and Delta charge. At $400 in added fees, a round-trip on Delta between Atlanta and Los Angeles would be cheaper if your bike flew as a passenger.
Credit: Bicycling Magazine