I would recommend audiobookshelf for the audiobooks, especially if you have your stuff running in docker. It seemed to me like the solutions to force Plex or jellyfin to do books were a bit more hacky than I wanted.

No clue about specific deals but I’ll share a site that I found thanks to Lemmy that had some good deals when I upgraded to an 18tb HDD for $180 USD.

https://serverpartdeals.com/

YAMS.

https://yams.media/

Not perfect, but if you just want the ding dang thing to start so you can see what a working setup looks like, then bam. Use yams.

I use Kavita for my comic book collection, and recently added some books into it as well. Syncs well across devices. I don’t really read books as I have so much time to listen to them instead but I can’t see why it wouldn’t work for someone who does.