Having used CB recently for family communication it seems that a reasonable reliable range is:
Base station to base station with proper antennas : 10 miles
Car to car with medium sized antennas : 2 miles
Car to base station : 5 miles
Handheld (with helical antenna) to base station : 1 mile
This refers to UK CB radios (FM, 4 watts output, 27MHz).
Range can be more than this but if you want to communicate reliably this should give you a guide to whats possible.
CB radio in the UK no longer requires a licence and can easily be fitted in a car using a magnetic mounted antenna and a connection to the cigarette lighter socket.