I would not bother to explain now why in the long term the price of any product is determined by the income of the population and costs of manufacturing.
somebody slept through economics. prices are dictated by supply and demand. even if the cost of manufacture for a given product is cheap the prices can still be high if the demand out paces the supply.
since the earth (supply) ain't getting any bigger. and the population of the world (demand for residences) isn't getting any smaller. your basic economic law says prices will generally climb (barring local iregularitys like mercury in the water, high crime rates in your area, etc.)
BTW- What is the cost of manufacturing an acre of land?