I don't set aside a budget for books, but I tend to buy used/thrift/book sales whenever possible keeping things a cheap as possible.

Paper books for long term durability and reference. Ebooks for when I'm researching/writing as there are to many that need to be referenced.

I stopped buying books and started relying on the library when I realized that my local library was really well stocked. I started buying them again when they started being goofy with their hours (closed on long weekends) and their response, like all state institutions, to covid.

I would rather have a shelf full of unread books than an empty shelf.

I dispose of books by returning them to a thrift store for resale or to a charity that runs used book sale fundraisers. And I have let go of many books that I later regretted.

I buy books for two reasons 1. Research on topics that I want to write about - non-fiction, reference, text books. 2. Entertainment - paperbacks, pulps and vintage genre books.