soundproofing from noise above me?

Hey all, I am trying to soundproof my ceiling from noise above me - the girls there walk with heels on the hardwood floors all day long.... I completely took the ceiling off (sheet rock) and I now have the joists exposed and I can see the plywood subfloor under their floor. I would like to soundproof between the joists and leave the joists exposed (I love the look of it). What will be the best way to do it without burning a hole in my pocket? Thanks!!