I forgot to add that the size of this is also good for propping the books on as a portable desk.
I realize the irony of using a “big box” store to source parts, but these days sometimes that’s the only practical place to find some stuff.

I was told once that 75% or more of things donated to thrift stores are immediately thrown away and never make it to the sale floor. If a project like this is to your liking, perhaps making friends with thrift store staff could get some good free or almost free raw materials.