At my favorite club in RI, they offer 2 for $25 dances on Sun - Tues day. Most everybody that works those days charges this fee but some girls say that they charge more (i.e. 2 for $30) and one girl that might have recently left, said she didn't like 2 for 1s but would do it if I bought her a drink (I would ahve paid a tip, so all is good in the end). However, on the other days and at night, I have gone in many times and said to the girl that I am used to do dances for the 2 for 1 price and can they do somethign for me. Some will offer 2 for $40 (house fee on Sun-Tue day is $5 for set whereas house fee rest of the time is $5 per dance - you pay the dancer and she pays the house, so dancer makes $10 a dance Sun-Tue day and $20 a dance rest of the time. So, 2 for $30 when it is not 2 for 1 also brings the dancer $10 a dance), others will do 3 for 2. Well over half of the dancers that I ask will do dances for less than the $25 per dance when it is not 2 for 1 time, so I ask. Worse that can happen is that they say No. Of course, I have an excuse, the girls in general know I come mostly on the 2 for 1 days, so I am simply be honest when I ask.
Now, regarding CR, the price is $100 to dancer and $30 to house for 15 minutes. I have only seen one dancer offer a better deal although I have heard of a few dancers offering a BJ for $100 total but that is not the norm. Generally, they have a menu if you want extras and these are almost always negotiable. One girl even quoted me $100 extra for a HJ and $200 for a BJ but if I didn't have the money, she would do the BJ for an extra $100. I am not sure how that is negotiation as she offered her standard rate and then immediately reduced it but depending on how busy it is, most girls will come down in their standard rates for extras.
Sorry, long winded answer that essentially says, you can always ask but you run the risk if you get too many NOs, the girls will avoid you altogether.