It is hard to put a concrete number on our recommendations, which is why we use the more open ended labels "beginners, casual, intermediate, and advanced". However, a decent approximation may be:

Beginner: 400 - 1200 Elo
Intermediate: 1200 - 1600 Elo
Advanced: 1600 - 2000 Elo
Expert: 2000 - 2200 Elo

Master: 2200+ Elo

It is hard to put every player in the same "box". One beginner may find use in a beginner or intermediate course, whereas another beginner may be well advised to stick only to beginner courses. Similarly, some Intermediate players may feel comfortable with Advanced courses, and so on.