There is not something such as a stable earning for a cam model. The same cam girl can do $50/h a month and $5/hour next month and $100/h next month. This could depend on very few whale customers she get or she loses, and by how many new camgirls and/or customers are added to her main site(s), and so on.
Very often I see a cam girl getting a whale-boyfriend, some of them make a deal with the camgirl such as: I take you in private every day most hours you are online, but then you don't take in private anyone else - the girl accepts if she gets like $2k or $4k or whatever she deals with the guy. At times it is not a deal, is just the girl is too lazy to be online for more than this one guy who is sure cash.
Then this cam girl rents bigger apartment, buy car with mortgage loan and so on, and shortly after her whale-boyfriend stops, and she is broke immediately - she returns online at cheapest price for 12 hours per day shifts, with little results and cries for advance payments or loan even from the cam site
In fact I can see statistics of girl earnings are very unstable, even when they are online the same hours per week and month.
Extreme cases but not so rare can be a 10 times difference between different months.