Miss Idealiste -- The transport fee is HK 300 / month, which is HK 10 a day. Actually, it should cost her a little less than that to get to and from our house (HK 200-250 / month) but sometimes we send her out on errands, so the extra 50-100 is for that. She lives pretty close to our home.
Just a warning -- As Cara often points out here, having a live-out maid is a calculated risk. I don't want to encourage people just because we decided to take that risk. I've personally not heard of anyone being punished for it, but your contract will state that your helper lives at home.
We also agreed to it because
* She's lived in HK before
* She has a network of close family here, who helped her find a decent place to live
* She has a network of church friends here, who do the same
* She seems mature and stable -- she's married with a child back home
* She really seemed keen on living out
Another girl we were considering was much younger and had never lived in HK before. I don't know if I would trust her to live out. After all, if anything happens to her -- she gets sick, pregnant, etc. -- you are responsible.