You have to apply for a HK visa from the Chinese embassy in Pakistan firstly with the following documents:
1. Valid passport of the applicant.
2. Completed application form.
3. Return air ticket for Hong Kong and its photocopy.
4. Hong Kong hotel voucher of room reservation.
5. Income certificate or bank statement of the applicant.
As for the fee and more detailed info., please contact the Chinese embassy in Pakistan directly.
Here is their contacts:
Tel: 92-51-8255015, 8255016, 8255059
Fax: 92-51-2279600
24-hour Mobile Phone: 92-0300-5015865 (for Consular Protection)