I did some quick research and found out that Tungsten has almost identical
density as Gold, and should be cheaper since each light bulb contains
probably a fraction of grams. It seems to be the only non-exotic metal equal
to or heavier than gold. It will be very difficult to tell from density if
you get a fake coin which is gold plated tungsten.
However, given the extremely high melting point of tungsten (4000K), I don't
see a small shop can melt and cast tungsten easily. As a comparison,
platin