I'm a designer and am doing a project which will involve creating an artwork with thousands of coins.  This questions in two parts: 1.  Which coins would be the most cost effective to buy.  I need a silver looking coin and a brass looking coin. 2.  Where could I purchase these coins. (I'm watching bun pennies on eBay but feel there has got to be a simpler way to purchase) 3.  Naturally budget is an issue as with all projects of this type. I really don't want to have to use currency in current circulation.  Any thoughts on this matter greatly appreciated.