Am I the only one who sees the futility here of trying to answer 3 different questions simultaneously? It seems to me that the OP is grappling with:
- Should he/she fix the Civic?
- How to sell the Civic without passing smog (and other issues)?
- Best used car for $7k?
The most important question has still not been definitively answered:
WHAT’S ACTUALLY WRONG WITH THE CIVIC?*
dgerch, the absolute best path for you forward here is to figure out exactly what is wrong with your current car, and I’m not convinced that you have. You mention taking it to multiple places, that’s the first problem. Find a mechanic who you trust and is knowledgeable, or else take it to the dealer. That advice was already given, and you never clearly stated whether or not you followed it.
Get a thorough explanation on why the cat and battery pack needs to be replaced - ask lots of questions if needed, and get a detailed breakdown of the costs. For the cat, a P0420 code is pretty typical, but that absolutely does not mean an automatic cat replacement - it could be a bad $100 oxygen sensor. The battery pack, I’m a little less knowledgeable on. There is no such thing as a dumb question, and as soon as you don’t understand something, you need to stop the mechanic and ask them to simplify the explanation until you do understand it. Write stuff down, for goodness sake. Then, when you have as much information as you can possibly get, post it on here.
Btw, feel free to completely ignore all of this - I’m sorry if I come across as judgmental, but it’s crazy how many people come on here expecting solutions, and then completely disregard the sound advice that is given. The folks on here can absolutely advise you well, but not if you only feed them random bits and pieces of the story. A “new” car will not necessarily solve everything - it’s entirely possible for you to go spend $7k on a car today, and then tomorrow have to turn around and spend $2k on a new catalytic converter for that car (I’m guessing you were not planning on getting a pre-purchase inspection done).
Maybe I’ve been in engineering and/or academia too long, but you can’t possibly hope to make an informed decision unless you have all of the information, and (most importantly), you understand it! And if you don’t have all of the information (again, at the risk of sounding judgmental, it does not sound like you do), how can we possibly hope to have it?