The most effective way to get cheap clicks is to create your own custom audience (do some research about it, if you don't know it). Once you have your custom audience you can then upload it on facebook and target only those people, that way you'll get cheaper clicks as compared to relying on facebook targeting features.
To lower your cost per click even further you can keep the traffic within facebook, if your website has an SSL Certificate (https) then you can use plugins or apps to integrate your landing pages on facebook tabs, then send the traffic to that FB tab.
When you keep the traffic within facebook, FB will lower your cost per click unlike when you're sending the traffic to an external website. Other landing page building software like LeadPages make the integration really easy.
Also use Facebook Retargeting to increase conversions. Retargeting is basically remarketing to the same people who showed interest by visiting your FB tab or website. The more they see your Ad the more likely they'll buy.
Hope that helps