I'm currently at work buildinga camera obscura. It will probably have an aluminum pole frame, hexagonal, with some kind of light-proof fabric stretched over it. It will have both a pinhole aperture and a lens and mirror periscope system that will project onto a viewing table in the middle. My question is, where can I find bulk quantities of light-proof fabric that won't break the bank? Hopefully, the fabric will be black on the inside, white on the outside, and ventilated. Any ideas?

"Not break the bank" is the issue. For smaller quantities, darkroom cloth would be the answer. It used to be widely available at well stocked camera shops but you'll have to hunt for it now. I think it came in 36" wide bolts. It was not cheap, at least not cheap enough in my mind for your project.

What comes to mind insofar as cheap and light tight is concerned is heavy black plastic tarp material, probably available in bulk rolls from a builders supply. While I have not tested it, I suspect it is light tight. It will not meet your other requirements, but I expect it would be the only inexpensive way for you to build your project.

Historically, camerae obscurae were actual rooms (the phrase means "dark room"), and thus they were built out of solid materials as opposed to fabric, so the many problems I foresee with this project, among them instability in wind, light and water leakage, and insufferable heat build-up, would have been obviated or mitigated. Think of all the disadvantages of a tent.

Yes, I have considered all the disadvantages of a tent. However, my goal is for this to be an easily-portable camera obscura that can accommodate up to three, maybe four people at a time. I would love to build a more solid, permanent structure in the future, but the parameters of this project will not allow it. This is actually my senior project (sort of an undergraduate thesis) for school; I have a window of about 8 weeks in which to work, and a budget of under 300 dollars. And so a building is just not feasible. I would just convert a room in a building into a camera obscura, but that does not fit the portable requirement.
And so I'm back to my initial quandary: what fabric to use?
Thanks for the advice though!