Are they trying to steal the car? buy "The Club", that will discourage them from breaking in because they cannot steal the car. Are they breaking in to steal something out of your car? Don't leave anything of value in the car where they can see it.
The club is available at most department stores...
I looked it up at AutoZone, there are a couple models but it looks like a cat converter is between 350 and 400 bucks for that car depending on the model etc.
If its intermittent, it could just be a bad or dirty battery connection or the starter solenoid is going out. check out the battery and ground connections first.
It sounds like a vapor/liquid separator that connects between the vapor canister and the fuel tank. it keeps liquid fuel from entering the vapor canister. (charcoal canister). That's about all that thing does.