The boys do NOT set the price. The customer does. And the rate is pretty much the same whatever bar they come from:

1,000 to 1,500 baht short time
1,500 to 2,000 baht all night

Less if you're not happy, more if you're over-the-moon.

If a boy tries to demand or set a rate, or tries to suggest that "XXX Bar boys are more expensive", give him a pass.