go visit a machine shop (look it up in the yellow pages). Tell them what you need - most likely they will have the aluminum on hand (only certain types of aluminum bend well - they should know that though). You will only need one bend. They will use what is called a bending brake. They might charge you for the Al but might give you one bend for free if you're nice. You could even call ahead to see if they have the Al on hand.
I would expect you could get what you want for around $10. If they quote you much more than that, it would be

Good luck.