I've got a couple of aircraft for my Russian Civil War forces, but hadn't yet gotten around to building my own flying bases - the few times they've appeared on-table I've borrowed flying bases for them.
I got a telescoping mechanic's inspection mirror cheap from Canadian Tire (an auto parts store), some 3" plywood craft discs from Micheal's, and washers and alligator clips from the hardware store.
Photos being worth a thousand words, etc, here's a compilation photo of the initial assembly of the beastie.
The base is two 3" wide plywood discs stacked. Before gluing I drilled a wide hole in the bottom one to accommodate the bolt head, and a smaller hold in the top one to pass the bolt through. The top edge got bevelled off with a wood rasp and smoothed with sandpaper. The two 2" fender washers got tacked in place with superglue, then I ran a bead of Gorilla Glue around the edge and pressed some gravel into it.
The mechanic's mirror had a base that unscrewed to reveal an M4 threaded socket, so a 20mm M4 bolt up through the bottom of the base will lock the telescoping stand in place nicely.
Up at the top end I unscrewed the swivelling mount that held the little round mirror, used sandpaper and a file to roughly square off the ball joint, then tacked an alligator clip in place with superglue. To properly secure it, I lashed it in place with fine wire (see the top left photo) and then saturated the lashing with more superglue. It seems solidly gamer-proof, and it was a much easier method of securing the alligator clip than anything else I could think of!
The alligator clip needed to have it's handle bent outward slightly so it would open just a bit wider - the screw in the belly of my White Russian SPAD is right at the limit of this clip's jaws. I'll have to use smaller screws from now on! The little scrap of balsa wood on the handle is to make it easier to open the jaws all the way, as the way it's mounted means the stand gets in the way of your fingertip otherwise.
The whole thing cost about ten or twelve bucks; if I had washers and other bits around to scrounge (a more complete shop setup than I've got, in other words!) you could do it for not much more than the cost of the telescoping inspection mirror.