What is the average cost to replace cat converter on a 2002 Toyota Highlander 4-cylinder?
Unable to answer. It depends on two factors. (#1) the cost of mechanical labor in your area. (#2) the cost of the part itself (new or salvage yard).
FIRST you find out why the OLD converter failed. If it's oil fouled, a new converter won't last long and you're just waisting money if you just replace the converter. If the converter is oil fouled, you'll need to rebuild or replace the engine first. Other than that, it's usually best to cut the exhaust line and weld in the new converter.
The life of your catalytic converter depends on the condition of the engine and the fuel you're using. If the fuel has the wrong additives, the catalytic converter can become plugged up. If the engine burns oil the oil vapor will build up on the catalytic converter and it can become plugged. Otherwise, if the catalytic converter isn't plugged, don't replace it.