Incase if your family are already in Doha (visit visa) you need to pay the following:-
Visa transfer fee (from visit visa to family visa) - QR.500
Initial Visa fee - QR. 200
Blood Group & Photo - QR. 50 (Approx)
Medical Commission fee - QR. 100
RP cost - QR. 500

Incase if your family are still in your home of country they are planning to come family visa you need pay rest of above except Visa transfer fee (QR. 500)