Yes the front car on the driver's side decided to check out. As a result the "service engine soon" light comes on occasionally, and the engine cuts power at 3500 Rpms or so, thus making freeway driving tricky. Dealer wants $2400 for repair, small repair shops don't really want to touch it as it requires removal of the engine(the cat itself isn't removable, the replacement part is a manifold with pipe and cat inside) and I'm out of warranty. Any thriftier solutions to this?

You have to remove the engine to do the cat on this car? Wow....that's a terrible design. So much unnecessary cost. I don't know of any other options other than finding a bigger private shop that is willing to do this...

Are you actually over 80,000 miles?
There is a federal 8 year/80k mile warranty on emissions components, and especially catalytic related parts.
If you have records of this happening at any point before 80k, I'd be knocking on Infiniti's door.

Aw man, too bad it wasn't the passenger side. That one can be changed without pulling the motor. (RWD only)

I would try disconnecting the Y-pipe from the cats and see if you can clean it somehow...like cleaning coils on a A/C unit, maybe you can spray it down and let it soak.