Depends if you want to buy one, or make one for a third the price.
I'm using 2 atv gun racks, one for each side. And using binding straps to strap the boards down.
Main thing if you make one yourself, don't allow any metal from the sled to touch your board.
The gun racks I'm mounting on each side towards the back of the sled, then right behind where the passenger feet will go, I'm mounting the binding straps. The straps will literally 100% circle the binding so I had to attach an ankle strap and toe strap together. You also want to make sure that the padded pard of the binding is holding both edges of the board or else you'll slice up the straps.
Made one for my last sled, but am struggling to come up with a good design for the new 2012 M