Not so fast. First off, you might not need a catalytic just because the light is on; second, you can't really bring your own parts to most repair shops, as they will not guarantee their work if you do that.
I'd suggest that first of all you get a firm diagnosis that the catalytics (there are two of them) are bad, and depending on what that says, then go to an independent shop that is not a national chain store.
I saw the catalytics online for about $625 apiece, so you'd best be darn sure they are bad.
Rockauto doesn't list them.