The Relationship Between Supply, Demand and Price

The person spending the money gets to decide the value. If i go to wall artand i see a bag of brown rice, and it's 17 dollars and 99 cents for a five pound bag of rice,. I got a decision to make. Do i value it at that same level? Probably not, and probably nobody else is either. But so these are, these things are such common phenomena that you don't even think about it most of the time. Must people onyo think about the relationship between supply, demand and price?