This is known as Inflation. The costs of production goes down with mass production and improved technologies. But once an industry matures, the scale of production does not give much economies scale any further nor does significant technological advances take place rapidly. Then the costs may not go down. On the otrher hand, as the depletion of natural resources that are finite and exhaustible takes place, the cost further extraction of such resources rise leading to rise in costs of production. Most important however is the balance in demand and supply. If demand grows faster than the supply, inflation has to occur. As more and more people try to buy the same limited supply, they will jack up the prices by bidding for the limited supply goods.
Finally, when technological progress is halted by foolish policies by the Govts., like in India agricultural productivity is low because govt. does not allow large scale farming saying that they want to protect small and marginasl farmers, food production will rise at lower than the growth rate in demand supported by both income and population growth/. Similarly, monopolies and oligopolistic cartels like the OPEC have successfully jacked up the prices of crude oil.
So, you cannot assume that prices will go down with time and technology and mass production. Economics is not as simple as the people would like it to be. Sorry for saying the hard reality and unpalatable truth.

What you’re alluding to is a phenomenon known as inflation. This process is usually mediated by an increased quantity and/or velocity of money relative to the GDP, stress on natural resources and land, and changes affecting the relative value of currencies on the foreign exchange market.