You can keep 1 male and 3-4 females in a 10 gallon aquarium. Personally, keep a male in one enclosure(a small rubbermaid) and circulate the females through the males enclosure to try to control the pregnancies. And I like to have seperate enclosures for 'birthing'. As far a price goes....the cost of the initial mice, weekly costs of bedding and food. Thats is about it. THere is alot of mice breeding info available on the net....just do a quick search..you will find all you need to know I also use rubbermaid tubs instead of aquariums to cut down on costs.
i do like daniel mentioned. I use tubs and will rotate one male for my mice and rats...this way you can kinda controll what you will have when and try and form a steady operation for your needs.
www.ASFRats.info African soft-furred rats information and exchange.