how much it cost to repair the Cadillac converter and get a tune up and smog

Well, if you mean the catalytic converter, that depends where you take it, and what they use, and whether it is a California or Federal model. There are a lot of variables. The catalyst assembly is about $300 aftermarket, or one can be welded into the existing pipes. California models are much more expensive. Tune up is around $250, I would imagine.