Didi, ASHP's comments very much mirror my own. The fundamental point is I treat them like "real people". Too many of their clients treat them like a commodity, or a less than equal person (read Unique's posts and you will get an idea of what I mean, especially the less than positive way he uses "Pro"). Most the women I see on a recurring basis charge in the 200 to 300 dollar per hour range, some a little more, some a little less--a lot depends on the city, but age and looks and class all influence it.
I will set up a 3 hr session the first time. Dinner someplace quiet and reasonably nice, maybe a drink afterwards, then back to my hotel or her place. Almost invariably the "3 hrs" turns into more than that, but that's her call. 2 hrs out and 2 hrs in is more the norm, but never expected. Second time, again 2 or 3 hrs, time to talk--ask about her as a person based upon things she said the first time, etc.; maybe a movie or a walk through a park followed by hot chocolate and a pastry before the bedroom play. I treat her like I would any date, any I find the extra effort, attention, and SMALL extra cash is almost always well rewarded.
At that point things vary. Several times one has shown up with an overnight bag the next time, and asked if she can stay--in that case the extra time is off the clock. If I am particularly interested in having her stay, I will ask if it is possible, and how much it would be--typically her web site price is 6 to 8 times her hourly rate but what she quotes me is often significantly less. She knows I am not going to expect to spend the whole night fucking, and I will treat her like a date, not a piece of pussy.
For those I have been seeing for years, all rules are negotiable. There are a couple I never talk money with at all. I pay them the 3 hr rate plus meals/activities/travel if appropriate/often a gift or two, and it's open ended--a few hours, overnight, or a weekend at a cabin by the lake. They know I will treat them fairly, I know they will treat me fairly as well. One stays with me when she is in town, and considers the room and meals sufficient, but I know her well enough that I let her stay there even when I am out of town, and I stay at her place when I'm there for work.
Sorry I don't have a simple answer for you, but it's all about chemistry, respect, and trust.