This one is a little trickier than the Screened Bottom Board. It is reversible featuring both a 3/4" entrance as well as a 3/8" entrance. For this project you need a piece of pine at least 59 5/8", or similar scrap at a width of 1 7/8". In addition it uses 3/4" exterior plywood. Using all new material and my personal favorite 7/8 rough pine, you can save a great deal of money on bottom boards. To give you an idea.
Exterior Plywood 3/4" - $36.52 (Home Depot)
Rough Pine 1'x12'x1" -$13.80 (Home Hardware)
Not including tax we can make 12 solid bottom boards for $50.34, or $4.20 a piece.
Now simply cut the rails to the required length using a chop saw.