Information On Gerbils Please?

I want to be a professional Gerbil breeder so I have a few questions... About how much money does it cost per litter? Should I leave the male in or take him out while female is pregnant (I heard that you should and I also heard you shouldn't)? What are some good protein food that I can give the pregnant female? I need any other information that you all got please. Also, I don't want to hear that I shouldn't breed Gerbils or that there are enough Gerbil breeders because I know plenty about Gerbils and I own some too. I am really going to dedicate myself into breeding Gerbils and I will make sure that at 6 weeks the babies will get good homes :). Thanks