AFAIK bikes are just considered a regular piece of luggage on flights outside of North America. It still has to meet luggage size/weight restrictions though I think, which means that it will technically be oversized.

That said, the most I've ever paid to travel with my bike (on domestic/US flights) is $45. Keith is right, it's totally up to the discretion of the check-in counter person. I don't think I paid anything extra when I went to Singlespeed Worlds, and that was on Air Canada who explicitly state that bicycles cost extra AND you have to pay if they're over-weight (which mine was by 1lb since I stuffed a lot of extra stuff into the box) and/or over-sized.

I never understood the fact that you have to pay for the bike AND a fee if it's oversized. Unless you're travelling with a clown bike (or folder.. or break-apart..), it's definitely going to be oversized. Ah airlines.. always up for milking every last dime out of you.

Of course, golf-clubs travel for free!