A bit off subject (but not completely since Frontier is one of the main airlines serving Bellingham, and the only one that can provide a non-stop flight for me).
I checked Frontier's bicycle policy today. Bicycles incur no special fees, but they do count as an item of baggage, which may or may not cost you depending on your ticket class (at worst $20 unless you have two other pieces of luggage). Great news is that oversize fees do not apply to bicycles, so as long as your L+H+W is less than 110 inches, it's just an ordinary piece of luggage. If it's above 50 pounds, there's a $75 excess weight fee, so don't pack a lot of extra stuff in with the bike.
Bottom line is that if you pack your bike in a box, and all your gear in a disposable duffel, and keep each one under 50 pounds, you'll pay only $20+$20 for luggage if you have an economy ticket, and nothing if you have a higher-class ticket.