how much should I pay for a new cat.converter

you can buy a aftermarket cat cheeper than a factory one try a muffler shop.

These typically range in PA from about $50 for an aftermarket cat to upwards of $200 for an OEM-style catalytic convertor. One possible problem is that an aftermarket cat which does not have the same flow-through and same catalytic properties of the original can sometimes cause Check Engine lights unless the ECM is recalibrated as discussed.