My SA experience (so far.)
I've been on SA for about 6 months and here's my limited experience. My impressions is that the standard rate for an ongoing arranement is $3000 per month which includes meeting every week on a regular basis. Don't forget if you go out for dinner, movies etc you would be expected to pay for everything on top of her fee. Make sure you both agree to what is expected in an arrangement especially when it comes to the sex.
I am not interested in an ongoing arrangement. My requirements are quite specific. I want them to host (in other words we meet at their place), pay per session (PPS), $300 for 2 hours (negotiable). That's it. I'm not interested in meeting for coffee, lunch, dinner, traveling together, buying gifts, etc. If I was, I would use a dating site.
Most women on SA want an "ongoing arrangement" and would reject a PPS arrangement because it make them feel like a prostitute.
If a women does not host then your alternatives are a hotel or your place. Both unacceptable to me. A hotel would add to the cost.
There are too many young girls on the site but there are some nice 30-40 years olds if you search. (I am 61).
I have had luck with 2 women who were accommodating to my requirments and we had a great time. But it took a lot of searching and rejecting.
My advice is know what you want and ask the girl what they want from an SA arrangement. That way you can quickly get to the point without wasting each others time or broadband!