I spent some time online pricing pre-1964 circulated silver coins this weekend. by checking online sellers as well as ebay.
Silver dollars seem to have way more premium over their spot silver value than other denominations.
Old dimes, quarters or half dollars seem a much better bargain for those looking to acquire.
A roll of 20 "good to fine" Kennedy, Franklin, or Liberty halves can be had for around $170 (including shipping) on ebay. A silver equivalent of ten Morgan or Peace dollars seem to be selling for around $220 and up. I saw similar margins in price difference between dollars and halves at MintProducts.com. Other online sellers I checked seemed priced slightly to well above Mint Products' ask.
If you want to know current value of silver content in old silver coins, Coinflation.com is a great site for that.