1997 Nissan Pathfinder 153,000 miles service engine light on catelytic code runs great, just had new tailpipe & muffler installed. I'm told fixing this code could cost $1,000- 2,0000 is it neccessary?

If you work on your own vehicle, it would be $324.00 to $429.00 for the converter,at NAPA,if you even need one.
Unless you fail inspection for emissions, I would just have the codes read for free,write them down,look them up,then forget it, until I fail inspection a year from now.
That said,if the converter is blocked and causing you to loss power,then you replace it.
It is a bolt on item,check it out on NAPA web site.
Can not cost more than $80.00, plus part, to just bolt on. Have a relative do it in the driveway.