How much for parts n labor to replace # 4 cracked piston & rings

I would estimate cost to be in the thousands. It would require removal of the engine which opens up a world of possible extra costs. Also, the #4 cylinder may be damaged beyond repair requiring a new engine. Also, one would wonder what caused the piston to crack or the rings to be damaged. I would likely steer you toward a good used engine from a reputable source. Thank you, david@apexautoaz.com