Currently, we recommend clients to start with at least USD75-125/day per campaign & then scale based on performance & goals.

For users without a significant amount of data from using Facebook ads, it's tricky to define how much budget you require. It would technically be 50-100X the cost of the desired action (link click, lead, likes, engagements, sales, etc)

As per Facebook: Your ad set needs about 50 conversions per week for our delivery system to learn who it's best to show your ads to, and more conversions are better.

USD25/day is what Facebook suggests as the minimum budget for 1 ad set.