If you've ever used Vistaprint, you know you can get pretty good printed materials for not a lot of money. That includes postcards, business cards, and much more. I've experimented with using these for promoting my books, with basically no demonstrable gain. Part of the problem is finding good opportunities to distribute those, but one of my early mistakes was also not building in a way to track effectiveness. It's possible (albeit not likely) that I've made sales as a result of distributing some promotional materials in the past without realizing it.
In my most-recent experiment, I made a "large postcard" design that I planned to cut into parts instead of using as a postcard. One part is a bookmark to promote Two Boys, Two Planets and the other parts were designed to promote Assets, Budgets, and Credit: A Financial ABC. These materials now use custom QR Codes and URLs that will allow me to track whether I get any traffic from these materials. (So far, not yet.) The easiest way to do this is to use a link shortening service like Bitly to create a link that is only used on the printed material. If you use the URL elsewhere, you'll ruin your ability to see if the offline in-print promotion worked.
Of course there are other, even-cheaper (i.e., free) ways to market offline. One of my favorite free offline marketing stories was writing a promotional phone number in the snow and getting a call from somebody who saw it there. Free and very temporary, but it worked! If you have ideas for free or cheap offline advertising, please share what has worked for you in the comments.