Menger Sponge.

Size: 100x100x100mm
Walls thickness: 2~mm (all over)

Overall volume (the actual printing material used): 19.5cm^3
making this Menger Sponge the cheapest to 3D print for it's size on the planet! ;)

For Stainless Steel 3D printing i recommend i.materialise.com for their 3 types of surface color and ponoko.com