sorority dues

I think you are asking the wrong question. Chapter dues are one thing and room and board is a completely different thing. Chapter dues are not always set a local level, but might be set nationally for the sorority...it all depends and is not something that Panhellenic could tell you. You might also have to pay parlor fees as a freshman and any year you live outside the house. Some chapters might have a different name for this fee.
As far as room and board, you might try and call the office of Fraternity, Sorority and Cooperative housing. Doubtful they will tell you by name, but can give you an average. I think you'll find them to be in line with the dorms. I agree that it would be nice if the R&B costs were in your booklets during recruitment, but they are not. I don't think I would ask the question during recruitment either. Like boys and booze, that is not something you discuss.

I don't think how long the house has been on campus has anything to do with what the charges will be. Chapters that don't own a house and are going to build have executive offices that they work through for funding.

Anticipate, like joining any organizations there are going to be costs you incur. Joining a sorority is for a life time and not just the 4 years you are in college.

You will get all that information after bid night from the sorority. Panhellenic does not have anything to do with chapter dues. My house dues are paid by the semester and not monthly, unless you ask to have it set up that way.
Regardless of what house you join, the shirts, etc...are all going to be about the same. If you are worried about the costs, either get a job on campus (like many women) or consider not going through recruitment.