dude it's nothin at all, have a feeder tank, say feeders 10 for a buck, got some extra lunch meet well there ya go! it not much at all and they are the coolest fish you'll ever had unless maybe you get some caribe piranha.
Actually, it will add up on your expenses. The bigger these guys get, the bigger the appetite. Best way to go is getting an alternative tank and try to breed any kind of feeders for them. Plus depending where your located, you can always go to Asian markets where they sell beef heart, shrimp, krill, or squid for cheap.