You say that other producers entering the marketplace will cause the price to go down. Either you mean it will decrease the demand or you mean it will increase the supply. But regardless of how many producers are in the marketplace, bitcoins will be created at the same rate. Adding more producers does not cause the supply to increase and price to lower!
Bitcoin is more like a trading market where there is no fixed set of "suppliers" and "customers." There are buyers and sellers, and any given trader can move from one side to the other at various times without needing to build a factory or something. Cheap mining does not increase supply much in the traditional sense, but it does decrease demand, because would-be buyers can mine instead (substitution).
Cheap mining does increase supply somewhat, because difficulty increases as mining increases. But difficulty is calculated in hindsight, so with increasing mining the block rate goes up. Of course there is a fixed
total supply of BTC so any increase in the block rate now means a decrease in the block rate at some point in the future.