In this video, Homer has one peanut that he considers of great value because it's the last one that remains. But once he drops it and finds the $20 he is faced with a choice. He can get the peanut that he was longing for off of the floor and eat it, or he can use the $20 and go buy a few bags of peanuts. Homer chooses to take the $20 instead, but the opportunity cost is that even though he will get more than one peanut, he will have to wait a few minutes because he has to go all the way to the store, and there is always a chance that the store won't have any.
In this video the theory that "There is no such thing as a free lunch" is proven. Jerry's friend "gives" him a brand new suit and says he wants nothing for it, but then suggests that he is taken out to dinner at a nice restaurant. As a result Jerry has to take the man out to eat twice, and has likely spent a large portion of the cost of the "free" suit, on the man's food. When companies have sales like "buy one get one free" or "buy one get one half off" the consumer is never really getting that great of a deal. Yes, they are paying a few less dollars, but since the prices are already higher than production costs, the companies still receive a profit, and the consumer is still paying more. Thus proving, "There is no such thing as a free lunch".