What's The Cheapest Thing You Buy?

I had a rare dream I remember a couple of nights ago and one of the things I remember was discussing this question. Yeah, even my dreams are nerdy.

Anyway, I have still been thinking about it. You might say you can't buy anything for less than a penny, but unit cost definitely could be.  For example, a big bag of M&M's, each M&M costs less than a penny.

Now before we go too far here, atoms and molecules don't count! The rule we established is that it had to be something produced/manufactured by people to serve a specific purpose. Even this definition is tricky...how do you count a bag of sand? Sand occurs naturally, but if you buy a bag of sand, it has been sorted/processed to give a certain consistency.

But even given that, my answer I think beats even a grain of sand: transistors. Transistors are smaller than grains of sand and you can buy billions of them. You can buy an Xbox one for about $400 and it's processor has a whopping five billion transistors (that's just in the main processor...not counting memory and other chips in the system) for a cost of one eight hundred millionth of a cent per transistor! Seriously, two Xbox ones and you have more transistors than there are people on Earth for less than $1000.

Now this is kind of silly, obviously...you can't buy just one transistor for that price so you can debate whether or not that counts. Buying individual transistors from Radio Shack for electronics projects run a few cents to a few bucks depending on what type you need. I guess that's why we buy in bulk!

What is the cheapest thing you can think of buying? Curious if we can get down to less than the cost of a transistor?