Finding Bookcases that Will Last

I have had some problems with inexpensive bookcases not lasting. They bend and warp under the weight of the books that I put on the shelves. I really need to get some that are of better quality so my shelves will look nice and I can store all of my books. Can anyone recommend a good type that isn’t too expensive? I think I definitely need to get something that is made out of solid wood since this should be sturdier. I like being able to move the shelves around, but maybe fixed shelves would work better, I will have to look into it.