First of all, I wouldn't advise you to send paid traffic to a blog. Unless maybe if you have an optin form below each blog post, sidebar and maybe your homepage is a squeeze page. If you don't have optin forms below each post, on sidebar and your homepage is not a squeeze page then put your money in your hat, wear the hat, and hold the hat tight
Send paid traffic to a squeeze page not a blog post, but there's nothing wrong with sending paid traffic to a blog post, there are valid reasons as to why you might do it.
When it comes to FB Ads, then you need to build your own custom audience (google if you don't know it). When you use facebook's targeting options then your cost per click will be expensive, but with your custom audience you can get really cheap clicks.
To lower the cost even more, then you can keep the traffic within facebook by creating a facebook tab (there's a lot of tools for this). You can embed your blog into a facebook tab on your fan page and send the FB Ads traffic to that tab and facebook will lower your cost because you're keeping the traffic in their website and not sending them to a 3rd party site.
One last thing that I see a lot of people not doing is re-targeting, again, if you don't know it, google it. So use re-targeting tools to increase sales and conversions.
That's FB Ads marketing in a nutshell.
Hope that helps.