First, we highly recommend buying gold in coin form. They are easily liquidated, and the government that issued them is standing behind the weight and purity, which means you probably will need an assay to sell.
Remember, the smaller the coin, the larger percentage of its cost is in the minting process. The process requires use of machinery, and labor, so there is a small cost in stamping out a coin. However, it should be about as easy to mint a large coin as a small one, so percentage of price drops with larger coins.
The smallest coins out are about 0.5 grams, or less than 1/60 Troy ounce. These are not generally bullion coins, but are instead intended for collectors. However, with mints vying for business, most current bullion coins are being prized for being collectible, which could provide a favorable move in the value of the coin in the future.
The small size coins designed for small bullion purchases often come in 1/25, 1/20, 1/10, and ¼ Troy ounce sizes.
There are fewer mints making fewer sizes of platinum coins, but usually there are a few available.
Please consider these, which are currently available on eBay.
And, how aren't the platinum coins beautiful?
