The cost per lead on Facebook Ads is hard to determine because it can vary widely. Different factors like goal conversion rates, business goals, and budget caps all have an impact on how much you’ll spend on a lead.
Some common metrics for determining your “ROI” (return-on-investment) when advertising are things like Relevance Score, interaction rates with ads in general, click-through rate (CTR), and cost per click (CPC). Facebook includes filters that will show you “Lead Generation,” which is calculated by measuring the number of leads divided by an ad’s total budget.