I spent over $10,000 cash in 31 days there just on partying///girls.
Honestly though, you can have an awesome time and always leave with a pretty girl for about $100 a day. That's including food/drinks/taxi etc.
It really just depends on how you do it. When I spend 2 months there this year I'm going to try and spend $15,000 or less TOTAL...since I'm about to become a poor college kid.
The following summer I'll probably stay in Thailand for 3 months and since I'll be a poor college kid I'll be looking at spending under $40 USD a day...but it all just depends on how things pan out for me "work wise"...