There are a lot of questions here, and you will get some answers, but drying isn't a simple equation either, it depends on a lot of things.  For example, we have 2 bin sites, one on LP gas and the other on Natural gas.  If we are careful on the natural gas, we can dry our entire corn crop for 7 cents a bushel.  We start at 26% and finish with dry corn, so there is a variety of moistures that go in a bin.  When LP was expensive, we spent 26 cents a bushel at the other site, so we avoid using the LP if we can.  We have been drying in bin with natural gas, but have a neighbor that does a lot of corn with a big dryer that also said he spent 7 cents a bushel on his drying.