Why is osmium so expensive ? ? ?

From: Hans-Marc Olsen (mallet_riveter_at_yahoo.co.in)
Date: 11/17/04 

Date: 16 Nov 2004 20:27:43 -0800

I want to craft an osmium anvil to drop it on the head of my enemies,
because it's such a dense material.

But it's too expensive.

So what material is cheaper and can be used for my anvil?