There's one flying on a Super Cub which uses the following material, not pricey:
82" length of cold water type 3/4" PVC pipe and two Adell type clamps for attaching to aircraft
-gas welding rod to mount yarn on
-yarn
-length of 1/4" aluminum tube for color range markings
By the time someone has designed and built one, tested it, got STCs for all sorts of GA aeroplanes and marketed it, I'm still betting that it would be expensive.
Ian