Freight Baggage (Travis Po, distributed through The Freewheel bikeshop in SF) makes a case that is under the limit. I've used it with no issues, it comes out on the baggage carousel just like any other piece of luggage. The downside is that you have to take everything except the BB off the bike, wheels, cranks and fork all have to come off and if you use drops you need to bring them in a seperate bag. But you don't have to pay.

With a frame as small as yours I would think that if you take the wheels, bars, fork and cranks off you would be able to fit it in an undersized box.

No matter what you do, make sure you tape pads onto the tubes because sometimes they take it out for inspection. When I flew out of Chicago in May the removed my frame from the box and it looks like they slid it across the floor or something. I now put pipe insulation on all the tubes.