I would recommend the Royal Plaza in Mong Kok Kowloon. It is a nice hotel with decent facilities and good service. It is in a great location and is built on top of the Mong Kok East MTR station and also on top of Grand Century Place shopping mall so you can walk straight from the hotel into the mall in the evening and get some good food (I would recommend the Bali Garden).

The early bird rate (book 32 days before arrival) works out at $104 a night for your dates.

If not then use the priceline name your own price function and you can pick up the Marriott Courtyard for $70 a night (see Betterbidding results. Bear in mind this may not be possible considering your dates.