Bicycling has a nice article up on how to avoid excessive baggage fees when flying with your bike. They offer a nice breakdown of the best airlines to book with that charge the least for typical bike travel costs like multiple bags and oversized items (big box, bike bag, etc). Personally I’ve used some of these companies myself and it can save you a lot of money to pick a bike friendly airline.
Buddy Tip – If they the airline is charging you for your oversized bike box, usually the weight of the box doesn’t matter. Pack the box full of your riding gear and other bulky items so you don’t have to put them in your luggage.