If I was better at math I could probably figure out the algorithm for the perfect combination of Price, Service and Looks... It's rare that they overlap into the perfect experience... usually you have to sacrifice one of the three.
I have found that younger, gorgeous girls charge a lot, but don't have the experience to make it a really great session. They seem to just be capitalizing on their looks (and more power to them)
And then there are ladies out there, both older and younger, that I don't find attractive at all, but what they'll do and their advertised enthusiasm sounds like it makes up for it. (haven't gone there to find out though)
As for age, I've found in general, that ladies over 30, who've done this for a while are the sweet spot, they know what they like, what men like and how to deliver on both. Age doesn't always equal experience though, I've had a few lousy experiences with over 30, and I've met some 18-21 year-olds that just blew me away with their passion. I don't know if it's number of clients, attitude, sex drive or some combination but certainly YMMV.
Rate-wise though, if every guy out there had $600-$1000, there were wouldn't be backpage or HX or other 'malls' out there. But there are a lot of guys out there who only want to spend $200, so those sites exist. A $700 hr rate puts a lady's clientele into another socioeconomic bracket that the $200 crowd, and that's probably because she only wants to meet people from there. It could also be that she doesn't want to see that many people and prefers quality over quantity. There's a fine line between enough clients and too many, and every lady has to figure that out. For me, I'm not interested in seeing someone who sees so many clients they almost need a revolving door, but I also don't have illusions about only 1 a day either.
As I said, my sweet spot is someone over 35 who has been around long enough to know what she's doing, is still attractive enough to get me interested, and who fits with-in my hobby budget. Thankfully, I've found a few ladies that fit that description perfectly.
play safe,
DkG