Maybe do a little dumpster diving ahead of the airport? Nearly everything delivered to retail stores these days is in cardboard boxes. In the alleys behind these stores, there will be plenty of dumpsters with all sizes of boxes discarded for recycling. Just buy a roll of packing tape and box cutter for a few $ and fashion your own multi-layered box. I've built a few custom boxes for bulky stuff sold online - it's pretty easy.