Hello Charlie,

This isn't a matter of which platform is more affordable, it is about on which one you will find your target audience, followed by the quality or relevance of your ads for that audience. Speaking from my experience with Google Ads and Facebook it all comes down to this: The more your audience responds to your ads, the better cost per click or acquisition (or whatever your campaign goal is) you will get and, of course, results.

Having said this, these are things to consider when working on your campaign: Intended audience, campaign goal (awareness, consideration, conversion), budget, compelling message and offer, split testing, monitoring, adjustment, tracking, and retargeting.

Hope this helps,

Monica.