Wish I could add a picture. For my last of the season air layer I used the empty sundae container from Burger King. It's got the round-ish shape, it's clear, and it snaps together in the middle. Best of all, it's free...minus the calories for the sundae which I've got to pay for ;-(
I'm a reuse and recycle fan, as anyone who's had dealings with me can figure out. Earlier this year I gave a guy a fig plant that I had grown in a McDonald's cup. Of course he thought I was crazy, but, after a repot into something more aesthetically pleasing, his tree is doing fine.
For the sundae container I melted a hole in the top and the bottom and made a cut down the sides. Another option for the occasional air layer.