I'd say go for Chungking Mansions. It's a building complete with rooms for you stay, a mall and food chains. The price range of the rooms vary depending on the block. Try visiting their site.
If you're sure that you want to stay in 1 of the guesthouses/rooms. Contact them ahead of time so that they can book you. There are a lot of instances that they are fully booked. Oh BTW, All the blocks have different contact numbers.
36–44 Nathan Road in Tsim Sha Tsui, Kowloon, Hong Kong about 7 years ago