In the 80's when AM was put in the technical museum in
Europe licenses for AM stations were very inexpensive in the US
AM licenses were never "inexpensive" especially in major markets. As FM
became the major medium for music formats AM locked in on talk and sports.
If you want to listen to baseball, football, etc you are pretty much going
to be using AM...with the exception of some sports now being available on XM
and Sirius, the satellite stations. And when traveling the US mountain
west there are many many miles of highway where your only signal will be AM.
The FCC has been making very low power limited coverage AM frequencies
avaialble...and granted some of these may have been purchased by "kooks" as
you say, But the price of a radio station, be it AM or FM, has always been
determined by just one thing.....cash flow and profitability. No matter
what format, if it makes a lot of $$$ you can bet the price will be high.
And in the larger markets even if the station is not doing well the license
is still going to be pretty pricey as someone will buy it and hope to put a
format on the air that makes the big bucks.....