Generally its not a steady escalation of price… but then again (sorry) it really depends on what you want to do with the time.
Sitting around and talking and cuddling for 4 hours may be cheaper than multi-position intercourse with cunnilingus for 2 hours…..
Also a extreamly pretty young lady may charge more than a beautiful older lady (sorry, all ladies at Sherri’s are very pretty! from their pictures)
I would write to multiple ladies as not all check their messages on a regular basis and a few seemingly never check it. The more you write too the better an answer you may get.