Please give totems/nuts instead of dark matter thanks If you're worried about people not going to Ifrit after they have all of their weapons (though who would want to?) then make the No-Lamp chest drop materia, high level potions, and maybe a chance at HQ crafted equipment. Or items you can turn in for GC seals or something.

Also even if the drop rate goes to 100% the kupo nut amount required should match the inferno totem amount required. No reason for them to be more expensive.