It happened me quite recently and I just PM'ed asking, it was provided and on we went.
I think, if a lady lists "ask" then it is perfectly acceptable to ring/PM to inquire to that effect albeit "inquire" means precisely that as in if you accept the rate, then proceed and in the event that you don't, then give the PC answer, thank the lady, etc & move on although do not haggle, well I would advise against it as I would imagine ladies do not take kindly to it and you will be subject to a dressing down and some of the ladies on here are not pussycats when they are annoyed
I also feel that you would be able to have a reasonable idea of such depending on her profile- pics, reviews, etc.
Furthermore, I would agree with the poster above that stated it is largely irrelevant, I would view the profile, decide to visit, send a PM, usually only checking the price in the name of formalities. If I like what I see, I'm still going to visit irrespective of whether it's 100 or 150.