I bought quite a few of the Hemnes bookshelves[0] from Ikea. They aren't garbage pressboard, but also not terribly expensive. They actually replaced the garbage pressboard shelves I had that cost like $20 each, because I got tired of fixing up the back. The back panel is fiberboard, but it feels like HDF, not MDF.

0:https://www.ikea.com/us/en/p/hemnes-bookcase-black-brown-lig...