I built this one but for some reason the suction cups won't stick to my boat. Sticks fine on my buddy's 2010 LSV though, so I gave it to him.

About $35 in parts:

Handle/suction cups, $14 https://www.amazon.com/dp/B007VL3CB0..._zGeZzb1R7MG1S

24 x 12 x 1/2" HDPE, $17 https://www.amazon.com/dp/B000ILHWAM..._9IeZzb5GJ002X

2x 4" stainless machine screws, washers and locknuts
8x stainless wood screws
(I don't remember the exact sizes of the hardware)

I cut everything with a jigsaw and hole saw, and cleaned up all the edges with a trim router with roundover bit. The first couple pics were before test fitting on the boat. In the last pic, I removed the bottom corners to clear a body line on the side of the boat. It's set at about a 60° angle.