On the z3100, matte media uses somewhat less ink than gloss, and using gloss enhancer jacks up the usage even more. Twin packs of the inks (260ml total) run ~110 USD (gloss enhancer ~80).
Average coverage on gloss is somewhere around 1ml per square foot without gloss enhancer, 1.6ml with. Therefore, ink costs are around 45c a square foot, 75c a square foot with GE. For square metres, multiply by 10.7.