A couple of weeks ago ,I made up this shanty rack for my snowmobile in a little over a half hour,and under 8 bucks. Materials were just 2 large 5/16 thread u-bolts ($ 1.30 each) and two 2x3x8's ($ 1.99 each cut to length needed)a few wood screws,A few screw eyes for bungee tie downs,and thats it.
I just drilled the foot rest and placed the u-bolts on upside down, with the end of the 2x3 under the u-bolt strap. Add two 2x3 cross pieces, a couple of screw eyes, and that was it.
It won't work for all sleds, but it worked on this one . Cheap,lightweight, plenty strong,easily removeable,and simple to build.