It depends on the lady. You'll need to check the "extras" list for the lady you wish to see on the BOA website here:
http://www.blackorchid.net/nanaimo/home, by clicking on their name on their individual pages.
For example, I just checked three at random, and for MMF Emma is "Double reg rates", Ava is $220 "+ $60" extra for an hour, while Laya is "$300 (30 mins) / $ 500 (60 mins)". Some will likely have "No", others more, or less than the three examples.
I suppose it all depends on how comfortable the lady is with two random hard, horny guys.