There's always a catch... you have to work for it.
Go to Twiggie's plot (The Bug Shack) at Mithril's Anvil (27200,24900).
Cobalt Joints 349 units @ 7.5s per unit.
Cobalt Sheets 192 units @ 7.2s per unit.
Marble Blocks 119 @ 5.5s
Marble Keys 68 @ 6s
Obsidian Blocks 350 @ 4s
Obsidian Keys 102 @ 4.2s
This work will enable more silos to be made available for public use.