I bought this cheap electronic weighing scale off Ebay awhile back for £4.66 (about $7). For small amounts of gold, you probably need something with more precision. But for larger silver coins the scale is accurate enough and definitely worth the purchase at this price.
Ebay link: http://www.ebay.co.uk/itm/141808928684?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
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