Toyota Repair: Sienna catalytic converter question, muffler shop, california emissions

Question
Hello,
A co-worker is looking to sell his 1998 Sienna.  It has 86,000 mi. of hauling tools and equipment in and around NYC.  He told me that the last time he brought it to the dealer (where it has been maintained exclusively thus far) they told him that it would need a catalytic converter and without one he wouldn't be able to pass the next NY state inspection when it came due.  They quoted him $2,500.  He wasn't willing to put that kind of money into a 10 year old car so it is for sale, Very Cheaply!  I feel there must be a more inexpensive way to continue the life of this Sienna.
So here's my issue...
This Sienna is a "California Emissions" model. I have searched the net for a "California Cat" vs a "49 State" and some sites list that there is a difference between the two and some don't.  Some vendors have cats that say "for vehicles not to be registered in the state of California"  Does that mean I can use a "49 state" unit in a CA model and register it in my home state of NY?  Are they physically interchangeable?  More importantly, will it clear the code? My very trusted mechanic who has kept my current Previa going strong with over 206K tells me that 50 of the time aftermarket Cats don't even clear the code.
I don't want to go too cheaply and have to do the job twice but if the $2500 dealer job is the only way to fix this, this Sienna isn't going to be such a great deal after all.  Please give me some advise on this Cat issue.
Keith

Answer
Yes there is a difference between the CA emission model and the federal emission model, you should replace the cat with what the car was designed for and that is CA emission standards, I would recommend contacting a local muffler shop or chain store such as Midas mufflers, they can weld in the correct cat converters at less than half of what the dealer quoted. Without knowing what the trouble code is I don't even have any idea if replacing the converters is going to correct the problem, maybe you can let me know what the trouble codes are that would require cat replacement.