How much does it cost to fix the catalytic converted on a 2003 Hyundai Tiburon?

Don't ever use the word ballpark at a repair
shop or keep harping on prices or you may
& should be asked to leave
You can use your computer to look up parts prices
on hundreds of sites.
You don't replace any converter until you know you
have no engine cylinder misfires,proper fuel pressure,
fuel trim,no vacuum leaks,including exhaust,good or
new oxygen sensors
There is a reason why a converter fails
At 14 years of age ,sure, it's worn out, replace it.
Replace it your self