Mist,
the maid does eat the same thing as us la. but my estimate is rough. I based it on, if I don't cook, I will need to buy packet food for her right. So let's say budget is $3 per meal. then x2 (lunch and dinner) is $6, then say $1 for breakfast is $7 for food. so one month is $210 for food.
Then others leh.. cos once the maid comes, everything will go up. Water and electricity. Cos she will wash and clean more (than before you have a maid).. so everything will go up. Then you buy a bit of stuff like sanitary pads, toiletries, etc.. so may not need $400 la. But if she falls sick, u pay for medical to GP now is about $25 to $30. So some months maybe $300, some months $400 bah.