Any $150 repair would likely involve replacing just the cat, as opposed to the entire assembly. They would cutoff the old one, and weld a new one in place. The greater assembly has 2 pre-cats as well (see attachment), so you would want to be sure the problem is with the main cat if you go this route.
Back to your original question for a moment:
You cannot buy a used cat because it is a FEDERAL crime to sell a used cat. The law passed in the early '90s as part of a larger clean air bill. However well-intentioned, this law is completely absurd. If a used cat passes emissions, what exactly is the problem? Talk about a waste of natural resources and precious metals.
Pop Quiz- Which causes more damage to the environment?
a) Re-using a perfectly good cat from a car that was in an accident.
b) Mining for Platinum, manufacturing a new ceramic core, forming a new case in a smelter, and trucking it to it's final destination.
c) Encouraging those who cannot afford a new cat to circumvent emmissions laws.
1986 300E 5-Speed 240k mi.