i've traveled a bit with bikes also, and didn't find it too bad. i usually just use a cardboard box, and the most i've ever been charged on a domestic flight is $80 each way. When i shipped it, i think the total cost (with a lot of extra clothing and camping gear for "padding") was $50.
i took my mtb with me to guatemala in january, and TACA took it for free on the way down (i had one other bag as well).
on the way back, i was told that the US no longer allows cardboard boxes to come in on international flights (i'm thinking something was lost in translation somewhere along the line... that sounds kinda ridiculous!) so i'd have to pack the bike in plastic wrap. yes, plastic wrap.
the bike was fine, probably better than when i shipped it in the cardboard box!!
have to say, though, if i traveled with my road bike (which i plan to, eventually) i'll invest in a case.

