How hard is it to replace the crossover pipe on.

It's bolted on. Replacement is not too hard but access is real tight in your body style. We don't get involved with costs here because there's way too many variables. We don't know the typical labor rates in your area. We don't even know which engine you have. Failure of the crossover pipe is very rare so it's possible your mechanic is going to install a used one from a salvage yard.