First question... is your target audience there? Do they *click* on the ads, knowing facebook is inherently dedicated to tracking, profiling and reshaping society to it's NoCal dream? I sure as fuck would not click a facebook advert for porn; I know the next 5,000 adverts I'm shown would be shaped by that.
Last year I advertised a game for (normie) gamers on Facebook and Reddit; spending ~1-2k on each, so not massive amounts of cash. Both have failed to prove a positive ROI, despite constant tinkering with creatives and messaging. The mobile industry has turned this into an art-form, but you usually don't have the attribution tracking to duplicate it... and even if you did, just how did we as an industry manage to move from being a scalable one (where the up-front cost is fixed), to a commoditized one (where we pay Facebook $5 to get a user that hopefully will make back $5.10, and has no loyalty to us). It seems to be a *really* great business for Facebook... not so much for us.