If you really consider buying traffic, then you better have a budget for that because simply spending on ads will not make you much money, because you will have to test a lot before you see any profits.
Of course, the best traffic is the organic one since it is the most targeted one and the good thing about is that you can actually get it for free from Google and other search engines. You just have to work on the SEO, it does take time to get good rankings but it is well worth it.