Let's just refuse to get bogged down in "can't." Probably none of us will be able to take advantage of every single tactic mentioned in this thread, but surely everyone can take away at least one tactic they can use.
Taberstruth started with a virtually "free" way to market - by marketing yourself, your voice, your credibility. This takes some time, but it does work if you do it the way Taberstruth describes.
Let's discuss one limitation with this approach, and how to overcome it. I operate several informational websites (which don't sell anything) which are unrelated and which I don't connect in any way (it might muddle the "brands"). Years ago, it was okay to use a totally silly avatar name, or just your first name - no one expected you to reveal your legal name, address and phone number to all the potential stalkers of the world. This was actually one of the draws of starting an online business. But now, there seems to be a growing expectation - driven by Facebook - that you should use your real legal name or you are a bad, naughty person who is up to something. (This is distressing to me both as a web visitor and a website owner, but that's a whole other topic.)
My solution thus far has been to use variants of my first name, which is common, and nothing else. Of course, this kicks me out of using Google+, and there's no telling what other limitations it will create for me going forward if this obsession with real names continues. How would any of you suggest developing an authoritative persona without revealing your real name? Is there a better solution than what I've been doing? Like, maybe I should incorporate or set up DBAs, so I'm using real legal entity names? (Hint: in most states, incorporating is not very expensive, and setting up DBAs is very affordable.)
And in the spirit of the thread, I would add a few elementary ideas:
--Go to hobby niches to observe how people brilliantly but accidentally market themselves. Look how they use forums, blogs and social media to spread the word about stuff just because they love it. You can get some great ideas about viral marketing from this.
--Get very creative offline. Got a site that reviews restaurants? Find a restaurant you genuinely love, give it a genuine rave review, and ask the restaurant if they would post a sign with a link to your review in the window (bonus points if you can make a great looking poster that blends with their decor). Got a site that sells something obscure, like blueprints for remodeling homes? Ask Home Depot type stores if they'd put up a poster, or just recommend you to people who wander in thinking they want to remodel but aren't sure what they want. Look to businesses and social areas where your customers are likely to be, but that aren't in direct competition with you.
--If your site is for a local business, get customers to review your site on Yelp, FB, etc. Offer a coupon if you have to.
If you are getting into online advertising, Adwords is not the only game in town. Some others are much cheaper, and will give a very decent ROI.
Consider getting a good banner ad made, if you can't do it yourself, and buy some banner ads from related small sites and blogs. You may be able to trade the ads for something other than money.