Thanks for the info. I've found some interesting information for small airports. For example:
Dryden Regional Airport (Ontario, Canada):
Under 21,000kg: $2.95 Domestic, $5.05 International (per 1,000kg)
21,000-45,000kg: $3.80 Domestic, $6.50 Int'l
Over 45,000kg: $4.45 Dom, $7.55 Int'l
Min Fee (domestic): $10.30
Min Fee (int'l): $17.50
Unfortunately, there is very little information available online about larger airports (at least, that I have found), and very little of what is available online is about US airports.
What little I've found comes from a Atlanta Business Chronicle article from Sept 22, 2003. Apparently, at the time, JFK
was charging $5.25 per 1,000lbs, Dallas $2.23 per 1000lbs, and Atlanta had contractual agreements running from $0.46 to $0.93 per 1000lbs. So it is quite varied. I guess a good rule of thumb would be about $2.25 per 100lbs, but that's not based on anything close to a represenative sample...
Again, thanks for pointing me in the right direction!
Those who fail to learn history are doomed to repeat it in summer school.