Cheap Coffee
The cost per cup depends more on how much you throw out as stale, having sat in the pot for hours, than on the cost or the way you brew it. With good coffee, it will not sit around in the pot. Yes, it matters how you brew it, but rich fresh coffee requires less grounds in the filter and less will be wasted.
As long as you buy good fresh coffee the cost of a cup of coffee comes out about the same for pricey specialty coffee or for low priced coffee -- between 22 and 25 cents a cup. You might as well buy the good stuff and enjoy what you drink, as well as protect yourself from harmful chemicals. Buy fresh roasted, organic, mountain, single source Arabica and enjoy.
Incidentally, the same applies to decaffeination. There is an organic water process versus a chemical process. It is worth paying the difference for the organic.