Another simple principle is that buying in bulk is practically always cheaper. Most dealers offer a lower premium per ounce (or whatever unit of weight you measure) when you buy a certain amount of ingots at a time. In general, the best deals on gold coins are found on large retail websites that sell gold and silver coins and bars. The price per ounce decreases if you buy in bulk.
Always use the method described above and you will never go wrong when searching for the cheapest gold products. The main reason why gold cartridges aren't the cheapest way to buy gold is because they're not as popular, so private mints don't sell enough cartridges to bring the price down. The cheapest way to buy gold is to buy it in ingots, krugerrands (a South African gold coin) and sovereigns. For large gold investors or traders, gold bars may be a good investment and one of the cheapest ways to buy gold, but for the individual investor, due to the things mentioned above, they may not be a good investment.
At first glance, gold bars seem to be the cheapest investment when buying gold; however, unlike buying gold coins, a person would not get a discount if they bought in bulk.