The smallest premium I have seen on the American Eagles Silver is ~$3 per coin. Obviously when the market is in demand premium go up.
When dealing with bars, the higher the volume (1 Kg) or (100 Oz) the premium goes down per ounce but, it will be in less demand to resale.
I am of the opinion to call reputable wholesalers and see if they offer any discount for "a large investment" purchase. One company I have dealt with for many years is