check engine light is forever on

Hey Yaw...........(can you tell that I'm from the South)? I have a 96 Chevrolet Camaro with a LT-1 and six speed transmission. The car is a sweet, however; it has one problem that is driving me nutz. The check engine light stays on. I have put it on the computer and it tells me that I have a bad sensor on the exhaust. I have been told that there are several sensors on the exhaust and I have changed a couple of them. Problem is that they are about 90 bucks a piece and I can't afford to change them all. Here in N.C. I have to do an emissions test each year in order to get my registration and each year it costs me about 400 dollars to get it past emissions. About 60 miles or so afterwards, the light comes on again. Anyone have a clue of what I can do to get this thing repaired.