It's nice but the calculations are inverted. We know younger, prettier models can command better rates than "mature" models, usually.
And frankly, if it's $3K a month, it's easier to work as a secretary earning at least that, plus you get annual leave, benefits, medical, etc.
Anyone working for himself has got to earn a lot more than what he would earn in a corporate job, else what's the point of giving up the corporate benefits and assuming all the risks of self-employment?
I think most professional models know how much they should charge, they learn very quickly that they are not charging enough to cover the rent, they either raise their charges or exit the industry.
It's the weekend/part-timers we see on CS who have no clue on how much they should charge. They think they should charge $150 per hour, they want $150 per hour, but they do not have the skills and attitude of a professional model who charges $150 per hour.