How much to rebuild a 904 trans?

I was wondering how much it would cost to rebuild a 904 now a days. I dont know that much about making 904s stronger or shift kits but I hear you can do a lot with the wimpier 904. I'm not going racing I'll either have a pretty much stock 340 or a pepped up 318 in this Dart I have so I just want something for a street machine.