Sure, there are two chains in the system.
Honestly, if they are willing to do it for $400, I'd run with it as that is a very fair price (book time is closer to $600). It is not a difficult job if you do these regularly, but it isn't a good job to rough your knuckles on if you aren't in the engine bay regularly.
The oil pan, valve cover, and all front covers will need to be removed to access the chains.
It's a tough call with the next step... if $400 gets you on the road again and everything is fine, I'd keep the vehicle personally if it isn't giving you any other issues. Remember a $400 bill one month, another $400 4 months later, etc is a lot better than a $300-500 payment every single month :)
The big thing is if you feel safe in the vehicle. If you have lost confidence or fear getting stranded you will sleep better if you move on.
I'd stay away from the Prius (joking aside) just based on its end-of-warranty-life costs. I have run across far too many that have had extensive electronics issues once outside of warranty, and nothing that was 'hybrid' warrantied. And then 100k seems to be when the bills really start coming in on them.
I've heard nothing bad about the Subaru line as we spoke about before, but I do not work on them very frequently at all. I wish I had more information on them for you I just don't see enough to really comment though.
For staying in the same vehicle type, RAV4s do fairly well if they have been maintained; if you don't mind stepping up to a larger vehicle the Jeeps and Grand Cherokees are very low cost to maintain, and while plagued with the typical Chrysler electrical issues, it seems to be much lesser on the Jeep line.
Hyundai is a safe bet on new and just about everything they've made in the past few years as well. They have turned into quite the bulletproof company compared to 10-15 years back when we all sat around telling Hyundai jokes :)
Most new Mitsubishis are extremely reliable, however unless you are a good negotiator the price of admission is sometimes a little too high on them.... and I work for Mitsubishi... they just price them a hair too high.