If the cylinder is in good shape you can rebuild it. Napa has rebuild kits for $1 or $2 a cylinder. The kit is just the rubber components and the spring in the middle. I just finished rebuilding my front ones. I sandblasted the outside(ONLY THE OUTSIDE, NEVER THE INSIDE) Got a brake cylinder hone and honed the inside. Cleaned up the metal parts and painted the outside of the cylinder and they are looking brand spankin' new. I would look in to rebuilding them before buying new one, that will save you $30+ up front!
