Hey Tracey82,
Go to K-mart and they stock this cheap brand called BYS (I actually think this might just be E.L.F. rebranded). They sell eyeshadow pans and empty quads. I think the quads are on sale right now for $2.50! I picked up three of these the other day and they come with a mirror as well. Definitely fits mac refills. They're a bit cheap looking but who cares.
HTH!!