The coins of Renaissance Italy were mostly under 30 mm in diameter and extremely thin; they seldom weighed more than 4 grams [0.0088 lb]. [Perspectives on the Renaissance medal - Google Books]
Silver Blades
Pure silver weapons costs 20x the list price, affect monsters vulnerable to silver, but break as if they are of cheap quality.
Silver coated/edged weapons costs 3x the listed price, their breakage is not effected by the silver coating, but they do not do as much damage to silver vulnerable monsters.
See p. B275.
Silver Bullets
Bullets can only be solid silver, not just silver coated. Their weight is their cost, which is $60 per troy ounce, or about $960 per pound. [See ElliottWaveTechnician: The historical price of silver - from the Renaissance and figure $10 1988 dollars is equivalent to $1 1511 dollars, as per p. B27. Do not use the GURPS Loadouts: Monster Hunters, p. 13 calculations as they assume modern bullets (not solid metal spheres) and a modern price for silver.]
Lead Silver
Calliber Weight Cost Weight Cost
.33 0.0077 $0.15 0.0071 $6.85
.53 0.032 $0.64 0.030 $28.36
.55 0.036 $0.71 0.033 $31.70
.60 0.046 $0.93 0.043 $41.15
.62 0.051 $1.02 0.047 $45.40
Values are per bullet. Weight is given in pounds. (There are 16 ounces in 1 pound.) Assume these values include powder and wadding.