I think that you could get the same effect with trailer side marker reflectors that bump out, but are attached flat. Two wood screws and done. A lot less expensive and just as effective. Picture below is a light version but I've got the same thing only wider and just a reflector on my 24 foot car trailer.
If you really want to do this on the cheap go to a high end bike shop. By law in the US all bikes come with reflectors on both wheels. Nobody with an expensive bike wants to be seen with them - so most bike shops just remove them before build/delivery. I doubt anybody comes in to buy them. Many of the reflectors are pretty wide (maybe 6 - 8 inches). They'd probably give them to you for free or a couple bucks for a box of them. You could even glue two on top of each other to increase effectiveness and then use outdoor two sided tape and slap them on.
