On my recent trip to Vietnam I pre-booked at a hotel near Pham Ngu Lao street in Ho Chi Minh for 30$ per night. My flight was arriving after 10pm and I didn't want the hassle of searching for accommodation after arrival so I settled on this family-run hotel and made use of their airport transfer service for a further 15$.
When I finally arrived at the hotel after 12pm it was an oasis to me and I was satisfied with the queen size bed and clean, fresh linen and that's about all I got for my 30$ per night. Oh yes and breakfast which was a no fuss choice of pho or an omlette.
During the course of the next day I went to a restaurant to order a salad to go and i happened upon an american expat and we got chatting about accommodation and rates. The name of the restaurant is the Royal Saigon and the three floors above the restaurant are the guest house.
I would strongly recommend the Royal. For 13$ a night I got so much more than a queen size bed and comfy pillows. Each room has it's own computer and internet and massive flat screen tv with cable. The rooms are air conditioned and cheerful.