pipe

I just had a repair on my 04 vw bug and my mechanic said that my "flex pipe" was broken and causing some CEL lights to throw and he told me to take it to a muffler shop to get it repaired. how much do these replacements cost on average? with labor and everything.

This pipe runs just along the left underside of the engine, and it's leaking a light brown, dark yellow fluid. It has no scent, and this leak just started today. I haven't driven the car since Friday. The Haynes manual doesn't identify this pipe anywhere, and I'm at the end of my rope. Help me...