that's crazy. i lived in a two bedroom villa in chiang mai and my bill never went over 1000, and i don't conserve. i'm assuming you use a/c every day, correct?
just no a/c. maybe try hiding the a/c remote??? or a fan for every room? fans a quite pleasant with the windows open, i don't get hot at all and they run all night. also, very romantic to have blowing. you get a strong oscillating kind and it just blows over the bed.
if i needed a/c that much i would question whether thailand was for me, but it's up to you. kind of like liking wine in thailand i guess.