It's about (was) $5 a pound, but that was a few years ago. I believe the minimum was 5#. I have a small tumbler, so I use about 2# but you can share with another reloader or get a larger tumbler. Good luck.
I've been using the stainless steel media for a couple of years now. It's a one step operation, the primer pockets are perfect, the brass is shiny, cleaner than most new brass. No throat deformation, just clean. And the steel will most likely last forever. The tumbler is very quiet and can be used without annoying anyone else around.
Is it a powder? More coarse? What would you compare it to?
It's actually tiny little pins, small enough to fit through a primer hole and about 5/32" long....about the size of pencil lead for mechanical pencils. They are stainless, but they can be picked up with a magnet....must be stainless coated. The letter "I" on your keyboard is a close reference.