I've been told my 1996 Toyota Camry Sedan, 220,000 miles needs a new catalytic converter.

How much should this run price wise? How would I know if that is truly the issue?

Does it pass emissions testing?

Cost for the converter is $150-250 depending on what engine you have. Labor is probably $100-150

If it did pass the emissions test, then your catalytic converter isn't bad. Although if it failed the test, you'll need to replace it, as Brian has stated. Brian's right about the prices, although you'd probably be better off money-wise if you go to Advance or something and buy the cat and do it yourself, although you might be better off having it professionally done since the bolts are probably insanely rusted and are very difficult to remove.