Getting more results for your money is what is meant by "cheap advertising on Facebook," not spending $10 and paying Facebook less. Facebook prefers to display ads that users like, so if your ads do well—that is, have high engagement and click-through rates—it will reduce your costs. Advertisers use engaging creatives, target less expensive placements or countries, and frequently use video or engagement ads to warm up audiences before retargeting them for installs or sales in order to cut costs. Reducing your effective cost per click or install—rather than going over your budget—is the aim.