What with, brass buttons?

You could borrow books from your local library, if they have e-Library loans.

I happen to know on good authority1 that if you go on certain websites of the Swedish variety, you can find lots of books available for download. Like, tens of thousands of books at once, already converted for the Kindle, ready to load into Calibre. They frequently tend towards fiction and genre fiction, but that is not universally the case and unless you reading tastes are very esoteric I think you would probably find stuff that's interesting. Some of the collections available for download are, if you were to amass the same thing in paper form, at least the size of a good-sized home library. And there are big non-fiction collections floating around there as well. The morality of such things is best left to the meditations of the reader, but in weighing the utility of the Kindle in the abstract I don't think you can just disregard their existence, any more than someone weighing the utility of the iPod in 2001 could disregard the existence of Napster. The only problem you may run into is that most true scholarly content (papers, journal articles, most publications) will be PDFs, and the Kindle really isn't the best for reading them. The iPad is somewhat better because the screen is larger, but honestly I don't think there's an ideal device for them on the market right now other than a computer; you really need a display about 8"x10" at minimum to view most PDFs without reflowing them, which is bigger than most tablets. 1: Possibly from the same guy who everyone seems to be friends with and always knows what the current price of weed is. Hell of a guy.

I'm a big fan of http://longform.org/, and they have a 'send to kindle' button that will mail things to your kindle directly. They're full of free to read interesting long non-fiction articles that sound like exactly what you're looking for.

Do you have a library card? I've had a Sony eReader for about a year and I have, so far, purchased one book. I check a lot of books out from my local library.

http://ask.metafilter.com/222668/What-with-brass-buttons#3219519 less-so for the PDFs because of sizing/zooming issues http://calibre-ebook.com/ converts PDFs to .mobi format easy as pie. I wouldn't know how to use my Kindle without it.

I've loved my Kindle for a few months and haven't paid for a single book. I've found that Amazon really push the Amazon store, but there are many ways to get material. Science Direct have a http://www.applications.sciverse.com/action/appDetail/297849?zone=main&pageOrigin=MyApps application, which will send papers in mobi format to your Kindle. I don't know if there are academic publishers with similar applications for different disciplines. I use Calibre to read my favourite http://manual.calibre-ebook.com/news.html sites and to convert books from PDF to mobi format (with some tricks to make the format come out well). Friends with large libraries of ebooks have also shared with me.

There's always the http://freekindlebooks.org/MagicCatalog/magiccatalog.html. Pop it on your kindle, and you can browse through and download just about anything from Project Gutenberg right from your kindle (with a net connection, of course). I'm on a Mark Twain kick right now and have been using the hell out of it.

Most UK libraries that do lend ebooks only lend DRMed epubs, which cannot be used on a Kindle and cannot (legally) be converted with Calibre.

You might run this question by your local library staff. My library started lending ebooks within a year of my asking about it, so you never know. :-) You can also sort Amazon's Kindle store by price, low to high. I've found some pretty amazing deals that way, like well-known non-fiction titles for $2-$3 USD. That's especially true right now--there are 500 books available for about that price as part of a new promotion, and non-fiction is a big part of that. Can you be more specific about the type of non-fiction works you like to read?