This topic has been covered so many times, along with the one about the general price of an appointment.
There are situations where negotiating the price of any service, not just a visit to an escort, may be acceptable.
However, I would find haggling with an escort over price, especially the ladies with a well established reputation for quality, to be insulting. It is a very personal service, and one which, when carried out by a top class lady, is priceless.
If you want to haggle, maybe go to Benburb Street or other location where the 'streetwalkers' inhabit and get a quickie. Just don't be too fussy where the action takes place.
In all situations, it's a mutual decision. Every woman has the right to charge whatever they want, and every man has the right to decide how much he is prepared to pay. If you don't like the rates, try someone else.