I'll note that for those severely budget-constrained, the older versions of The Perl CD Bookshelf from O'Reilly are really affordable. $4 shipped plus any applicable tax in the US, for example, is a good deal if you don't need the latest version. This doesn't support the authors and publisher as much as a brand new book, but it's legal and far more ethical than using pirated copies.
Here's what the second version of the CD Bookshelf included:
- Programming Perl, third edition
- Perl for System Administration
- Perl in a Nutshell
- Perl Cookbook
- Advanced Perl Programming
There are also some good books that are actually gratis for personal use in electronic form. There's a huge GitHub project for free programming book lists at https://github.com/vhf/free-programming-books with various languages including English used for the lists. Of course there's a Perl section among many other languages and programming-language-neutral programming topics.