Funny thing, the price of silver is pretty closely pegged to the amount of labor needed to dig it out of the ground and smelt it, and that doesn't change too much without late 20th century technology being involved.
Transport is a big issue. The price of silver in 1550s Iceland, where there are no silver mines, was certainly going to be far higher than Joachimsthal where silver was mined and Joachimsthalers mined.
The Great Bullion Famine[1] and subsequent Price revolution[2] fueled by Spanish expropriation of New World gold and silver tell me that prices weren't so stable over the pre-20th century period.
