Using Pay Per Click ads is becoming less and less financially viable. This is mainly because they are an auction so if you win you’ll always be paying more that others thought the traffic was worth.
Also they are very expensive – $0.05 might sound cheap per click but unless you have a good conversion rate this quickly becomes much more per sale.
I’ve created a spreadsheet that lets you see how much per sale it’ll cost for a given CPC and conversion rate: