[9nGQluzmnq3M]

Tungsten costs around $30k/ton, so you'd be looking at a cool $15M for that 500T cube.

Lead goes for around $2k/ton, so this might be a more feasible compromise.

[brohee]

Depleted uranium prices are very hard to find, but should come as cheaper than tungsten.

Civilian sales look at least possible, I heard of at least one sailboat with a DU keel.