cost of acquisition sets a floor on price. Value sets a ceiling on the price. Supply/demand sets the price you pay. (in economics we further talk about curves - there many oil wells and some costs more to run than others, there are also many buyers and some value oil more. Similar for water where it is often free from a nearby faucet but people will pay a lot of it in bottle form anyway.
A bottle of water might be the same price as a litre of petrol, but the value is vastly different.
We don't pay for the value. We pay for the cost of acquisition (e.g. pumping the oil out of the ground).