How much should it cost to replace 2 catalytic converter on a 2005 Toyota Sienna

I heard some of Sienna having an issue with Catalytic converter and it's so expensive. My sienna has same issue. Check engine, VSC & trac off lights came on. Some tech told me that caused by using reg. or bad gas. but I use prem.gas. all the time. Those lights are on and off then solid. When the tech delete those error code with his com. then I can drive it for a while without alert lights. It costs about 1,500.00~2,000.00 in NOVA as I heard.

what are the codes, post so we can adv

For me, P0420