Speaking merely as a long time satisfied customer https://learning.oreilly.com/ (used to be called "Safari Books Online" back when I first subscribed) lets you get to electronic versions of all the ORA books as well as things from lots of other tech publishers as well as video courses. I've found it well worth what I pay them yearly that I don't spend on dead tree copies (then again I'm satisfied with reading things on my iPad).

Alternately keep an eye out as Humble Bundle periodically will have ORA pdfs in a collection (e.g. this current one; but nothing (directly) perl related in this one though).