Dahondude, your info does not apply at all times. I researched this before flying to Brisbane with bike in Sep-2011. Had extra luggage when packing sleeping bag and foam mattress for camping. Jetstar charged $23 for my larger case not exceeding 20kg (not a carry-on bag) and another $23 for my packed bike not exceeding 20kg. There is a size limit on a bike, so needed to remove quick release saddle and front wheel, but the fiddling thing was removing the front pannier rack. Left the rear wheel and rear pannier rack on. On the return trip, the packed bike fee had been reduced to $18, but the passenger fee had increased markedly. The other airlines were similar, e.g. Virgin had a dearer passenger ticket which allowed one to pack more 'free' luggage. Look at the airline websites, although some info is hard to find, or totally missing re bikes.
Some cyclists like a free box from a bike shop, but then you need some means of getting the box to the airport, and transport at the other end. Some major airports sell boxes for bikes. This means you would need to arrive very early at the airport to pack your bike. Remember that a non-folding bike is considered oversize luggage and passenger required to be at the airport 2 hours rather than 1 hour before boarding time.
For my circumstances, a bike bag was best. I bought a lightweight folding trolley from a shop in Rundle Mall -- not cheap but best for my purposes. Enabled me to manage the bike at both airports, store everything in a YHA cupboard, before I caught a train with packed bike to the country. Hired a large tent at the camping ground.