I just ordered the first shipment of silver source material to use for the first round of testing. With the price of silver in FRNs being near a year low at around $11/ounce, now is probably a great time to buy.
However, this source for the milled silver has a markup of over 40% above spot. I think its worth it, just to be sure of the quality. There's also additional charges for shipping, so the markup is approximately 50%. Hopefully the markup will be lower for larger orders.