I think that if you do 25 of silver you will find it will have to be priced stupidly high to cover the cost of the stamping process, stamps, and I would say the cost of design but that isn't a real cost per say because you do all the artwork yourself? If you don't have the design say .999 silver or .999 gold you could save the cost of the stamps by using the same ones for the gold and silver
Problem with using the same stamps is that gold and silver dont weight the same so a 1 oz silver coin is different in size than a 1 oz gold coin
Dont write the weight in the stamp either.
I can't believe I wrote all of that and it didn't hit me till you said that.... But regency mint can make you custom blanks of different width, depth, and length based upon a circle. The cost of their stamps was a joke when I checked a while back.
You could have one standard side for a gold coin, and one standard side for a silver coin in order to reuse the stamps and save some money.