I would like to create wall-to-wall and floor-to-ceiling bookshelves in a room, to hold several thousand books. The shelves for the larger books is in a grid like this, with vertical columns like in this picture:
Since it is many books, some being heavy, it needs to be strong, but as lots of material is needed, it should be cheap. It will be covered with paint and mounted directly to the wall framing. It shouldn't be as cheap a solution as found in this question What is the cheapest/easiest way to make bookshelves?, as it still needs to look like wooden panels covered in paint.
The 3 ft-wide bookshelf in my workplace collapsed as that was made of particle board, while supporting 30 three-hundred page textbooks, so I think this material might be unsuited.
What is a strong cheap wood or product that if painted looks like a plank of wood, that is really cheap, yet strong enough for holding a large quantity of books and won't bow?