How can I protect my loose leaf textbooks?

You could take the book to a copy shop, and have it binded properly (e.g., hot glue, hardback, etc.). Here in the Netherlands, that costs about 3 euros for a simple but effective glued back.

Find someone who has access to a document scanner and scan it. Our departmental copier/printer can also scan (I think the spec is 100 ppm), so 2000 pages will take a while, but not forever.

EDIT: Have you contacted the author to see if an electronic version is available?

In the olden days, you could buy little sticky circles that you'd place around the holes and this would prevent the pages tearing out of the binder.

Another approach is to put the whole thing in a box.

Or maybe scan the document and carry it around on your iPad – that's probably the modern solution.