Depends on the coin
type, but if you wish to get the trace metals and even the isotops, it definitely costs a lot. Many
ancient coins have lost the original composition from the surface layers and you need to drill a hole from the
side and use the turnings from deeper inside to get an idea of the original situation.
There is always variation within coin
types and between mints and dates so single coins might not tell that much. With both gold and silver coins I strongly recommend consulting the recent book by
Butcher and Ponting: The metallurgy of
Roman silver coinage. The techiques needed for accurate analysis require access to very expensive equipment.
If you only need results of high silver content (or gold) coins, then surface studies suffice and would be much cheaper. However, even then you need
help from a lab.
S.
Jyrki Muona