Something I've banged on about since I first started working with SEO is that Pay Per Click (PPC) is less effective than SEO in giving real ROI. PPC, are those "sponsored links" you see on Google, Bing, Yahoo, Lycos and even Facebook adverts are PPC. You pay for each click through and it can cost anything from a few pence to thousands of pounds in some industries.
The cost of PPC is huge and grows overtime to get the same number of visitors (shown below). The cost for SEO on the other hand, although starts larger will get lower over time and likely level out over time, but visitor numbers will continue to increase (shown below).
The infographic below shows why I will always promote SEO Services above PPC and why if you are paying thousands in PPC each month you should consider moving a proportion of that cost to SEO and get a more long term gain.