It's nearly impossible to benchmark this number with any accuracy because so many variable affect the CPI for Facebook ads: competition, demographic, season, and so forth. But I can tell you that the best way to figure out your own potential ROI, would be to create a bunch of different ads (using variations of images, colors, headline, body copy, and call-to-action) and give them $5-$10 budgets. That way, you can split test different ads against one another and figure out whether or not Facebook ads are going to deliver a great ROI for you. Your very worst FB ad may deliver satisfactory results, or your very best-performing FB ad may still lose you money in the long run. You won't know if FB is viable for you specifically until you give it a try. Hope this helps, Austin