Pay for link building? What? Yes, the different ways people do their link building vary from totally free to exorbitantly expensive, but one method a lot of people have not really considered is actually sending traffic that will build links to pages that deserve them.
There are different ways to use PPC to target your landing pages, but if you have good enough content you can use the traffic you attract to help create more links. The cost will vary based on the keyword you choose, but in some cases this can be very beneficial for your SEO.
Julie Joyce at Search Engine Land has 8 tips to help you fine-tune this approach.