Asking how to get free or cheap traffic is kind of a loaded question. First you really should define your goal for your site.
Also, what kind of site is it? Some sites are easier than others to drive traffic to. Proxy sites, for example, can gain massive amounts of traffic in a short period of time through just a couple strategic links and link spam. On the other hand, some niches may be very difficult due to over / under saturation, lack of interest, etc.
So, my advice, sit down, figure out what your niche is, what your goals for your site are, what risks you are willing to take, and how much time and money you are willing to invest. When you know the answers to those questions, it will be easier to determine a marketing strategy.