I generally go with the approach AB described, which is don't mention money. After a few drinks, just say I'm going, you coming with me? In the morning, give them 1000. On my my first two nights ever in LOS, I paid 2500 ST, which was over asking price, and 4400 LT, which was asking price for a FL who was hot in bed but generally a drama queen and pain in the ass. Then I learned and never paid over 1000 that tour, except when I wanted to tip.
I found that if you don't mention money, if they want more, then they will bring up the subject. On my third tour, much to my surprise, a lot of the girls were asking up front for 1500 Baht. I never paid more than 1200 that trip. For me, negotiating, talking money, really takes the edge off the fun.
The downside of not asking, though, is that on several occasions, I have got them back to the hotel, and then, after we are naked and in bed, they ask how much they are getting. At that point, I am really difficult to negotiate with, because if they piss me off and spoil the mood, then I would just as soon throw them out on their asses with nothing as f*ck them. On one occasion, the satisfaction I got from the look on her face, when I told her, "OK, then you can take your pricey ass and get it the f*ck out of here," was better than the satisfaction I would have got f*cking her. As she got dressed, she seemed like she still thought I would change my mind. Then I told her "There's the door, don't let it hit you in the ass on the way out." I have her picture, and I still get a laugh every time I look at it.
