Perday cost...is set by You. Idk how much they could cost if you like them just go wild. I set mine two ads at 2.00 a day, so I dont get a surprise bill.
I've used them with a couple of different ads. The ones that linked directly to my Etsy shop weren't nearly as successful as the ones that linked to my FB page. I haven't gotten any sales that I know of from it, but I have gotten more FB followers.
I used FB ads for about a month and went from 100 to 600 fans! I haven't really turned those fans into sales yet but at least I have more people to market to now. :) I think I did $2.00 a day.
I've used FB ads and can see in my shop stats that facebook has become a more productive traffic generator. I'm not sure if these equate to sales but it's bringing more views, for sure. And I'm almost to 1,000 fans!