Whatever amount of money you decide on I highly advise you to think again. Unless you have tons of spare cash and you don't give a hoot about what happens to your money or your Thai girl, don't give your Thai honey the lump sum unless you are planning not to see her ever again.
Because doing so will most likely cause her some pain and the final outcome will probably frustrate you. Handing over a large sum of money to your Thai girl could be a big mistake unless you follow certain tried and proven steps.
The major percentage of foreigners who link up with a Thai girlfriend are facing these kinds of issues. For example ; "How much money will she really need to cover her living expenses for one month?"
To answer that question you will need to consider several issues. One, of course, involves a bit of geography. Like, where will your Thai girl be living? Want to know more about this? What your Thai girl's pain is about and what the three things are that will cause the frustration for you and other foreigners with good intentions?
Myself and several friends who live in Thailand have faced these issues in the past. To help you avoid these problems I have written a detailed downloadable report on the sending money issue. The report is called "Thai Girls and Sending Money".
The report discusses 21 issues you should know about before sending money to a Thai girl. Check it out HERE.