If a girl is honest with herself... most chicks just want to make sure they aren't missing out on income. Opportunity costs. So... if you want to take a chick halfway around the world, and give her an amazing vacation.. and still be considerate of her missed "working" time, you might be able to find a catch for as low as 200$ a day.
Personally, depending on the friend I am going with, the other activities, and knowing our personal play habits(fucking a lot or a little) - I can accept anywhere from 250 a day to 800 a day given that all expenses are paid.
Both sides just need to be reasonable and communicate expectations up front. Boy, you won't believe how much I have traveled this last year.