Best price for a 2nd hand car

I'm moving to Okinawa this august and my employer is insisting that I purchase a car for convenience. I really didn't have a plan on buying one thinking that I could just use the public transpo (which they said, nonverbatim, sucks and unreliable) but will still give it a shot on the first few months. I'm thinking of getting one once I get settled in a month or two, or once I've saved up

1. Can someone tell me ranges of small car prices?
2. What are some important rules or laws (including insurances) should I keep in mind? I've read about shaken (JCI) but I also heard that there are other "optional" insurances but apparently I still need to pay for it. I'm confused.
3. Any tips on getting a 2nd hand car
4. Tips for a newbie driver in Okinawa