For starters, it's an 1870 , not 1970, 2 1/2 gulden, weighing 25g with a diameter of 38mm. 6.6 million were minted and each has a composition of .945 silver.
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Here's one sources estimate of value:
2 1/2 GULDEN (2 1/2 G on reverse, 0.76 troy ounces silver)
worn: $25 US dollars catalog value
average circulated: $40
well preserved: $100
fully uncirculated: $250
Source: http://coinquest.com/cgi-bin/cq/coins?main_coin=5163
Check your coin in the Completed Listings section of Ebay for current sales, not listings.
Don...
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