I came across
this yesterday. It may complicate things...
I like that he says charge less for the jobs you want to do and more for the jobs you don't want to do. Bottom line, set the price you are happy with if they accept and if they don't accept, make sure you are still happy. I'm sure that covers a wide range, if you are new I would just ensure it is a price you will be happy with if they accept! Also
this may be interesting reading.
I would actually quote him a price for the "model" $200 or whatever it is. If he thinks it is too high, he may want to find is own "model."
Like Tom said, if you really want the gig, throw x number of images in your pricing for them to use on how many every billboards they want.
Actually, the first questions out of my mouth would have been "what price range are you working in?" and "how many billboards are you looking to do?" The former lets me know if it is even worth my time to quote a price, the latter helps A LOT in forming the quote.