Do you know any hotel in Bui Vien area with good price?

For that price you are really only going to get a hostel.

I thoroughly discourage a female travelling solo to stay in a cheap room.
Cheap rooms bring cheap customers and friends.

You are Vietnamese asking us foreigners about a cheap place for your Vietnamese sister to stay in Bui Vien zone,right?
You know the reputation of this Bui Vien street?

Why not get her somewhere respectable,you pay $12 and she pays $12.
You'll know she's safe and comfortable at the same time.
Pham Ngu Lao street  is a good place to start,price wise.
Look up 'tripadvisor.com' to start your search.

Try Nguyet Van hotel, I was staying there for months, its safe, clean, reasonable price and serve nice meals

http://www.tripadvisor.com/Hotel_Review … _City.html

Bizu Hotel.

Greets,

(I might note that while Bui Vien itself is livelier with drunks, it is only a block away from Pham Ngo Lao, and in the Pham Ngu Lao district, as I am given to believe by the authorities.)

I know a couple of women on their own who have met with some success at small places. I stayed at a couple myself, noting the college-age visitors as being just people sightseeing. There is one place that apparently offers rifling your luggage while you're out, which I think would be more the risk of staying in a small private place in a poor country, but the others guests I've encountered seem not as shady as the loons in the 23/9  park; I'd worry more about the families/friends who have access. For Viets it may be different, but there's little disincentive from taking advantage of foreigners who are notably unaware of the local wiles. The Pham Ngu Lao area itself may be overall better for its higher profile- the exposure may make them watch their steps better (save at that ngoc place, it seems.)

Watch for the thieves on scooters. They're pretty active, having scored a few in the past week as I hear.