A man goes to a Home Products store to make a purchase for his house. He walks up to the clerk to ask about costs.
The man asks: "How much for 6?", "3 dollars sir" replied the clerk.
"Well, how much for 12?" "That will be 6 dollars, sir"
"OK, then how much for 200?" "That's 9 dollars, sir."
What is the man buying?