I think all depends on many things :
What is your budget for an hotel : 700 or 3000 bath/day ?
How many beers you drink/day?
Do you want to make some day trips?
Do you want a BG in your bed every night? Keep her with you all your stay, so pay for food, drinks, trips, gifts ?
Do you need to rent a car, motorbike or to use thk-tuk a lot?
In LOS, you can spend a lot of money in bars, girls, trips... but you can also have a great trip for cheap IMHO
I would say, for example, if you are rather quiet :
Hotel : 1200 bath
Food (breakfast, lunch and dinner) : 500 bath
tuk tuk or motorbike if you like to move a little bit : 200 - 500 bath
Bars (if you drink 10 beers, pay for lady drinks and BF) : 1500 - 2000 bath
Beach (chair and water) : 100 - 200 bath
Day trips (an estimation if you do it 1 or 2/week) : 400 bath
"pocket money" for shopping, etc... : 500 bath
BG : 1000 bath
So, around 6000 bath/day