I love these kinds of arrangements. It is only available to men with whom I have GREAT chemistry but then it is awesome. But I am not "on call" either. You can only be as tethered as you want to be and I would allow this sort of agreement with a control freak. By the same token, I can guarantee my clients is that I won't try to interfere in their personal lives because I already know they cheat.
It is nice to have guaranteed income, at guaranteed times as well. I may be able to estimate at the beginning of the month what I will bring in in the four weeks but I can't know. The OP said that he can't see anyone agreeing to 2k a month but why not? 3-4 clients on that schedule and I am only seeing men that I know I adore, that I know will be a great time. Ideal working conditions!