Jason - hey, first off congratulations on the request - that's impressive and too cool. Good luck with closing the deal. Keep us updated.
You might try calling some of the photo processing folks in town. I am sure they have experience sizing the photos in prep and perhaps know some of the details you need to be aware of as 'your' responsibility. I am a novice at this type of pricing, so take my info with a grain of salt, but perhaps something will make sense.
I sold a photo to a publishing company for a textbook and got my pricing here (below), based on the terms of use publisher quoted to me.
http://photographersindex.com/stockprice.htm
advertising - for billboard, the choices seem funny, but after putting in some random number it gave me a message to put big size and qty 200 whatever that means..... anyway see results below
http://photographersindex.com/price-calc.dbm- this number is for 1 year contract, so I SUPPOSE you would just factor in only one month - not sure if that would be accurate, but read some of the term issues....
Type of Use:: Advertising
Specific Use:: Billboard
Press Run:: Over 100
Size:: Full page or Major Illustratio
Low Price:: $2,100.00
Average Price:: $3,550.00
High Price:: $5,000.00
Survey = 123
One Year Use, Reduce prices for 6 month use. Susan