PPC stands for Pay Per Click, and the most popular tool is Adwords from Google.
This tool is used if you want an immediate result for positions on Google, and it can cost as little as R2000.00 a month or as much as a million.
The more competitive the market you work in, the more you have to offer Google, which is set up in a bid system. So, the more people bid the more it will cost. You basically have to bid more than other companies per search phrase to achieve a better position.
Adwords can be totally unfeasible if done incorrectly, but on the other hand it can really give you a huge advantage if managed well.
See my articles for more information.