valley. (building construction). An inside angle formed where two sloping sides intersect. (geography). A generally broad area of flat, low-lying land bordered by higher ground.
In ordinary usage, price is the quantity of payment or compensation given by one party to another in return for goods or services.
The economic definition of cost (also known as opportunity cost) is the value of opportunity forgone, strictly the best opportunity forgone, as a result of engaging resources in an activity. Note that there can be a cost without the exchange of money.