My experience in this area has not been good.  Been in a couple of ripoff situations where the T-girl suggested I see her friend also for extra $$.  Two times ripoff, however, still = ripoff.  The one exception was a well-known duo consisting of a pre-op and post-op (Alessandra and Lenora??).  The price was reasonable and the action was very hot.  Only negative was one pop and I was outta there in less than 30 minutes.  

Anyway my advice would be to wait until you meet someone who is at least an 8 in performance and who is also GFE, and then ask her if she has a friend.