You are missing the connection that when you are negotiating the price down that the girl is also reducing her service although she is not telling you this. There is a very real connection between punters that negotiate down their price and then complain of shite service. Of course we don't want to overpay but I prefer to put my negotiating into finding out that she's an enthusiastic participant which deliverers far more value than saving a few bucks.
One suggestion might be for you to try the opposite negotiation. Be willing to have HJ for $50 but let her see that you have the extra money sitting with your phone. So now it's up to her to encourage you to spend the dollars instead of you hoping she will do more for less. It's a subtle difference.