The old spark plug non fouler plugged into the rear O2 port to turn the check engine light off trick, I'm actually surprised a smog tech actually looked and caught this. Anyways, the catalytic converter is a wear item, usually 80-120K they need to be replaced. I would just replace the cat and hope the car goes for another few years, it is a Toyota, I think odds are in your favor.

When you buy a new car, there's tax, higher registration costs, higher insurance costs, depreciation, loan interest (if you are financing) that should be compared against that $3K.