If you're looking for Pewter Alloys for your casting needs of Silver Pewter for jewelry making, you can buy them from Purity Casting Alloys Ltd, priced as follows (as of today July 18, 2016):
Pewter Alloy (Lead-Free) aka - "Britannia Metal" or "White Metal" - $16.35/lb ($1.02/oz)
Silver Pewter (Lead-Free) - $17.90/lb ($1.11/oz)
Go to www.purityalloys.com for the most recent prices.
If you're trying to find the pewter scrap prices from the local scrap yards, check out the iScrap App’s yard locator tool.
With many types and grades of pewter, most scrap yards will have to analyze it before giving you a price.
And if you're looking for the prices of different pewter pieces online, check them out on Google Shopping.
Pewter is made mostly of tin and over time, may develop a dark patina. This dark patina is expected and even desired and removing it may detract from the value of your piece.
Check out some tips that will help keep your pewter in fine condition at Howtocleanstuff.net.