Both use the same Facebook ad budget system, but deliver different results per dollar spent.
Boosting a post and running a full Ads Manager campaign don't really compete on cost, they're different products with different price structures. Both draw from the same Facebook ad budget system [1], but what you get for that spend is very different.
When you boost a post, you set a total budget (say $50 or $500) and Facebook distributes that spend over your chosen timeframe. You pay exactly what you decide to spend, nothing more. The catch is what you get for that money: limited targeting (age, gender, location, basic interests), no placement control, no A/B testing, and Facebook optimizes for engagement by default, not conversions. So a $50 boost might get you reach and likes but no leads.
An Ads Manager campaign uses the same ad budget system, but you're paying for precision.
The real cost difference isn't in the budget line item, it's in efficiency. A $50 Ads Manager campaign with proper targeting will typically generate better results per dollar than a $50 boosted post because you're controlling what you're optimizing for and who sees it. If your goal is lead generation, appointments, or sales, Ads Manager pays for itself. If your goal is just "more engagement," a boosted post might be fine, a point echoed in small business marketing discussions [2] [3].
If you're testing or only doing awareness, boosting works. If you care about conversions or ROI, you need Ads Manager. And if you hate manually deciding which posts to boost and when, Boosterberg automates the whole thing, you set rules once, proven organic content gets boosted automatically through real Ads Manager campaigns, and you pay $25 per month per page instead of guessing on ad spend.