BSE,
It would go back to the usage. The contractor will likely use the images for a much longer period than an RE agent would, so that will carry a higher price tag.
For lots of info about licensing and usage, hit up
John Harrington's blog.
For what it's worth, a full architectural day rate would start at $1300, and that would be a bargain. The top shooters (using medium format and with creds that make us all look like children) get more like $3200/day.
Good luck getting that out of your contractor, but just so you know where the market is.
Because of the usage involved, I take my RE rate for an equivalent shoot (in terms of time spent, and skill involved) and multiply by 2 or 3 for a builder that will use the images locally and on the web.