How much can they be worth?

Have to admit that i really enjoy the show (despite the last 2 shows which were obviously slapped together). I think Bobby Brown is a riot. However, watching him go on spending sprees, etc, makes me wonder how much can they really be worth? I mean, their "heydays" of moneymaking are obviously over. They seem to spend money without a conscience. Or maybe that was just while cameras were rolling...So what can 2 musicians bring in if they have, lets say, only 1 or 2 BIG hits in their careers?