Here's some free or inexpensive things I've done to get traffic, promote a brand, or both. Some were actually inadvertent.
1) Participate in forums or blogs related to a niche. I AM NOT TALKING ABOUT COMMENT SPAM FER CRYSAKES. But you can participate in discussions, offer your expertise, or ask intelligent questions; you don't even have to link drop. If you sound like you're worth knowing in the niche, people will come look you up.
2) Related to #1 - Go to seminars and webinars, ask intelligent questions, and engage. People noticed. I went to an advanced seminar once where mostly everyone was a beginner and I was an intermediate, so my questions to the speaker sounded like I knew what I was talking about. At one point someone asked for my email address and two entire rows wrote it down (I didn't think to bring business cards, d'oh)
3) Go where your audience is. If they're on Facebook, go there. If they're on LinkedIn, go there. If they're old school, go to the newspapers or magazines. If you can't afford ads, then offer these publications *good quality* content for free. They still need content too, just like websites. But you MUST find out where your audience is hanging out when they're not with you.
4) Partnerships with non-competitors looking to attract the same audience. One of my clients is the top reseller for a particular tiny niche of products, but it's one of those things that you never think of until you need it, and then it's pretty much too late. So he's partnering up with the manufacturer to create an informational website to raise awareness about the niche. We're going to create the site, they're going provide the content, and both companies will promote it.
5) Plan for repeat business. I think I've said this recently. If your business plan doesn't include a way to bring your customers or visitors back, and give or sell them something else - if your site is like a one night stand - you've lost half the battle. Even Google traffic likely won't fix them. Find a reason for everyone to come back and do whatever with you again, or find a new niche.
6) I shouldn't have to say this, but email is *still* one of the best channels there is, and you can build your list pretty much for free until you get into the thousands of contacts. There are tons of posts and primers about how to do it right and not spam. Seriously, if you have a good enough list, you don't give a crap about Google.
7) Make sure your stuff is easily shareable. Well first you have to give them a REASON to share it, but of course, we're all quality merchants and publishers, aren't we, so of course all our quality content is worth sharing. But put the frickin' buttons on. Your audience may not be on FB or Twitter, and of course it's not on Google+, but that doesn't mean they don't share - my largest B2B client's most used button is his "email this link" button - because people send the product to their bosses or their purchasing depts and ask for it to be bought. Your sharing buttons can just be email / print / PDF; it's worth it.