silvertowne is typically over priced. also they sell your personal information to "marketing partners" (unless you opt out, it says so right on their website).
the best way to compare prices across various products and vendors is:
https://comparesilverprices.com/ and
https://comparegoldprices.com/
however, you won't typically find the lowest premium listed there. the best way to find specials is to join a dedicated gold and silver forum such as goldismoney, kitco, bullionstacker, etc. there's usually a deals thread on each one and the lowest premium items will find their way on to any of those sites very quickly
typically the lowest every day premium will be found from jmbullion or provident for silver. for gold, ebay will always allow you to pay the lowest premium (stick with large dealers such as apmex)