Have just returned from Phuket and was paying 1,500 to 2,000 for ST/LT (low season rates). Of course it depends on negotiation and the time of year.
Apart from perhaps in Bangkok those Phuket prices exist nowhere else so you can discard them immediately.
Girls will always ask for a lot more than they're actually willing to accept, so don't ask. You need to play a little smarter than your average 2 week tourist with ungodly amounts of testosterone-laced spunk desperate to vacate his bloated testicles at any cost.
If you plan on staying anywhere for any extended period you have the advantage of time on your side. If you ever plan on bringing girls back to your apartment or room, be choosy.
A few years ago, while I was single in Pattaya, I met several nice ladyboys over a period of time who I had a short time with. I TOLD them how much I had available and they accepted, e.g. B1,000 including room. I also obtained their phone number if I liked them. I would send an SMS occasionally to one I liked saying "You want B500?". It wasn't long before they were SMS'ing me instead.
In a nutshell, TELL them what you are willing to pay for their services (within reason) or pretend as if that figure you suggested is all you have available. Be prepared to walk away. Try not to ask the girl directly how much they want as they will inevitably quote on the high side to the point where countering lower is an embarrassment on both sides.
If you start off paying too much in the beginning it is almost impossible to lower that cost due to having set their expectation levels. So start nearer the bottom, rather than the top, you can always 'tip' a bit more now and again.