It doesn't cost as much as you would think. They obviously have to pay the lease on the house itself, and that would include the studios for BOTS, camera runs etc. Then you've got cameramen, staff, production, presenters etc. The housemates themselves only get paid £30 each a day (at least they used to anyway), which is nothing. The biggest cost of any tv show is the actors and actresses...this can run into hundreds of thousands, but for BB they don't have these costs to pay. They'll be making money from the advertising revenue obviously, then they'll be the Lucozade sponsorship, competitions (although I doubt they make much from competitions). For a tv show, it probably doesn't cost that much to make.