For silver jewelry manufacturers, they usually base the cost of an order on the replacement cost of the silver. In other words, if you place your order and silver is at $14 per ounce, then it jumps up to $16 per ounce before you pay, you will usually be charged based on the replacement cost of the silver at the time you pay. In this case, if you hadn't paid until silver hit $16, you'd be charged based on that amount.
This system can cut both ways. If I think silver will be climbing, I try to pay as soon as possible, even if I don't know the final total. Sometimes I'll just wire some $$ to lock things in. I know of at least one wholesaler that buys silver futures in order to lock in prices. This can be an inexpensive way to leverage against volatility.
See a broad range of silver jewelry information at http://www.wholesalesilverjewelry.net.

