My relative has an 06 with over 200k miles and it's still running fine, although it did need some electrical component replaced recently that was a few hundred dollars, and the battery is a little degraded so it gets slightly worse mileage.
From what I've read, they're generally cheaper to maintain than the average car. You'll spend a lot less on gasoline of course, but also less on brakes since the electric motor takes care of some braking.
You can buy various products that bolt on to protect the catalytic converter, or you could hire someone to weld some rebar around it, or if you want to do it yourself, you can wrap it with chain or barbed wire.