On Tue, Nov 17, 2009 at 8:24 PM, William Donzelli <wdonzelli at gmail.com> wrote:
   I just
remembered. ?It's rhenium. ?$6000-*mumble* per ounce. 
 The most expensive thing I can think of is Boron - specifically the
 purified B10 isotope. I once had a pair of ancient neutron detector
 probes, with the inner surfaces coated with the stuff. The price makes
 gold look like dog food - $10K per gram, roughly. 
 
The Helium3 they use for microKelvin heatpumps for radio telescopes is
pretty pricey by the gram, but I don't remember the exact cost - it is
in the thousands-per-gram range, though.
-ethan