^ autotrader.com, magazines at local stores, just plain everyday car
lots. I',m sure its not that much different.

cars.com

local newspaper (best bet)

local dealership

autotrader

Georgetown is actually in Minnesota very close to the state line, and just north
of Fargo, ND which straddles the state line.  You could call it a suburb of Fargo.
Its zip code is  56546.
Put that zip code into a typical auto search engine:
http://www.autotrader.com/
http://www.sellmycar.com/
http://smartcarfinder.com/
I like to go to used car lots though.  Nothing like looking at the real thing.

Such magazines exist here too, and "classified ads" in the back of the
daily newspaper are also very popular.  Both will contain a mixture of
ads from private individuals and dealerships.  They'll also give him
good calibration on what various cars are worth in our market.

I like this book very much.  Some of it is about the relative
advantages and disadvantages of various means of buying used cars; and
some is about systematic consumer rips that seem generic to car
dealerships.
http://www.dontgettakeneverytime.com/
See also
http://www.ftc.gov/bcp/conline/edcams/automobiles/consumer.htm

Taking the prospective car to a mechanic for pre-purchase inspection is
a good idea even if you know your way around cars -- you are paying for
objectivity as well as expertise, since by that stage you already want
the vehicle.  This can also give you an idea of what scheduled and
preventive maintenance might lie ahead.

Note also that he'll want to get some local guidance about which cars
would be good in the winter, of which they get more than their fair
share.  Also local custom about snow tires vs. studded tires vs.
chains, etc.  

Cheers,
--Joe