Inventory input of items that are same price within certain days but different quantity.

Hi,

Thanks for reading my questions. 

May I know the user-friendly ways to input 4 different items that are the same price a, b, c, d within a certain period of time. However, the amount we order each time is different. It should have a date column, an item column (4 items), a price column (4 different prices) and a quantity column (everytime is different for the same item). That is, I can sum up the amount I spend within a certain period of time (price x quantity then sum up the cost to buy all these products within a certain time).  Since the price of each item is the same, may I know the way not to type the price? Is it relate to creat formula or many different ways to do the job? Any trick or shortcut? Thanks again.