I just had a universal high flow Magnaflow cat put on my car, and I passed smog. yeah in CA technically it's not legal to change the cat if the factory is working ok. There's an exception: if your cat was damaged and needed to be replaced b/c say you went over something on the road. But like other people have said: don't worry about it. Smog places in CA will just look under the car to check that you have a CAT. If they ask "why does it look so new"...say that you clean it regularly or that your last one was destroyed when you went over something. They're not going to ask for documention that the latter is true. BTW documentation can be provided because if your CAT was really was damaged, there's a form the shop is supposed to sign indicating this when they put on your new CAT. No one bothers to get this form signed anyway.
So just get the magnaflow cat or another high flow cat and have someone weld it on but make sure it's a high flow that is obd-II smog compliant like the magnaflows are. I paid $110 for my magnaflow cat. Whatever somthing costs, the dealership will just multiply by 10 and tha's their profit.
Hehe, I tend to be the smog person on this board.
Here is the magnaflow CAT link if you want info:http://www.car-sound.com/universal/430.htm
I know you need a CAT since your car has 230,000 miles, but don't listen to people who say it's not worth getting a high flow because the factory is already high flow. Uh-huh...nope there's a big difference looking at the design and looking at the features of the magnaflow. Without even knowing anything about it, it's a much smaller and tighter can in appearance. Everything helps in racing. Who says $100 for a CAT and $50 to weld is too much to spend?
Good luck with smog.
One more thing, be sure to get the right size, that is the in/out diameter to match your current exhaust piping.