Vehicle failed Emission Test yesterday with the following codes P0420, P0430. on 2004 Chevrolet Tahoe

What exactly does these codes mean, and what is the approximate cost of the repairs?

Asked by for the 2004 Chevrolet Tahoe
your catt converters are poss bad. they have to come from the dealer and they are pricey. approx 2500.00 parts and labor. you might want to have it ck'd by your mech because it might also be bad o2 sensors