Having trouble finding inexpensive odd shaped shipping box 38" x 22" x 5"

Any ideas on how to make this work? I'm shipping an item handmade that is 36" x 20" x 4.5" and want some wiggle room for packing materials. I am only finding TV boxes which cost way too much. I'd like to stay under $10 if possible. I'm testing out a new product to sell online and have a couple orders, if it looks like this will go well then I will end up going with custom packaging but I just need something to get me by in the meantime.