Help with a bill payment

It's probably an easy question to answer. But I want to make sure. I am an antique dealer in small items. I have just bought a collection of badges. This was for 2.7k. When entering it on the bill. Do I have to list every item? And if I enter the amount as expense Cost of goods sold. And then the amount. When I come to sell the item and have to put a new stock item down with cost and sales price. Will the books balance? Or will I now be spending ( in theory) twice. Thanks