I little suggestion if price of the books is an issue. You can buy PDF's from Paizo for much less than the books cost(especially the hardcover books), then print out the pages you need that will show your watermark to prove you bought it. It's also a lot less heavy than hauling all your books around everywhere.
Oh course, I've rarely seem anyone check to make sure everyone has all the books they need, even at big conventions. But any GM is well within their rights to call you on it, and say you can't use the ability or even play the character if you can't provide the books they are in.
And if you have an electronic reader (like a kindle), a tablet or a laptop, you can just show the source to the GM on that. But it still has to be a legal pdf source. Alternatively you just have to provide any source, if one of your friends has a physical copy of the product (maybe they are a subscriber) they can lend it to you and use their pdf.