Housing is the most expensive component of your planned 1 month stay. If you search for service apartments and YMCA, you'll find past threads that provide detail information on estimated costs.

To get you started, in Kowloon side, near Sip Kip Mei MTR stop, there is a very nice YMCA, with rooms that start at HK$7K and larger units for HKT12K a month.

Good luck.