You might want to go look at the Alliant Powder website and I'll provide a LINKY
to the relevant page. If you're buying bulk powder there will be some fairly stringent storage requirements. They're not necessarily limiting, but they are concerned with fire codes and licensing and that sort of thing. Basically, if you store more than 20 lbs then you've got to provide a container for powder storage.
I'm sure you could order a boxcar load of Unique and Alliant would give you a great price. I'm also fairly certain that the Fire Marshal would want to see your storage container.