Unlike most silver coins from the 1960s, this coin actually contains silver! There are 0.616 troy ounces of silver in this large coin celebrating the fourth term of President Stroessner.
Base value (BV) of the coin is 0.616 times the current price of silver. If silver is trading at, say, $17 US dollars per troy ounce (look it up at kitco.com), then BV = 0.616 x 17 = $10.50 US dollars.
Due to the unusual nature of this coin -- REAL SILVER -- there is a small collector premium added to the price. Here are some typical values:
average circulated: BV + $1
well preserved: BV + $3
fully uncirculated: BV + $7
eBay is a good place to track the current price of this coin. Be sure to use the 'advanced search' feature and review only coins which have actually sold at auction. Also, be sure to check the shipping cost charged by the seller and modify your price estimate accordingly.