What forces define how much an object cost ? Within a capitalist society the ratio between supply and demand define prices. The rarer and more in demand an object is, the higher it would cost. The unit price of a given good will varies until it settles at a point : the equilibrium of supply and demand. This is both magnificent and scary. It only works within a theoretical framework of a perfect competitive market (no monopolies) combined with perfect communication (all information for supply and demand is accessible and transparent). Unfortunately, monopolies exist and supply/demand information is manipulated.
Price is different from value. A price being the tag on an object put by its manufacturer or seller, while value is how much I think this object would cost. Price is higher than the cost of production since its seller need to make a profit. As a consumer, it is almost impossible to evaluate the cost of production of an object. The means of production have been made invisible with industrialisation and mondialisation. Culture-wise and space-wise. Thus, the consumer needs new points of reference to formulate value. Marketing is here to help to create virtual value to stuff we don’t need.