I'd like to know how much it costs to rent a place at an airport for
small businesses. I am interested in how airports charge their rent as
well - do they charge same rate per sq ft throughout the airport or do
have different per sq ft rates for different locations at the airport?

I am especially interested in how much it would cost for me to rent a
place to put a kiosk that will likely take up anywhere from 9 to 12
square feet (a little bigger than those internet kiosks). I'd like to
know how much will be to place such a kiosk at the waiting rooms (at
the gates where people wait for their flight). I'd like to know this
information for main airports in as many cities as possible, but
especially for LA, Boston, New York, Toronto and Vancouver. Monthly
rental cost per kiosk or per sq ft will do. Thanks.

You'll probably have to raise your price to get the detailed answer you want.

This is one of those questions where you need to contact the airport
directly and find the answer out yourself.  If you are thinking of
going into business it would be useful if started by doing this
yourself.