We have been looking at just the Additional Marginal Opportunity Costs of our choices. What about the total cost? For example, we see and hear ads all the time about different cell phones and cell phone plans. I spoke with a representative of one phone company the other day. She started off with this is the Price of the Plan per month for 2 years and this is what you get for it. Then she said 'but wait. if you add this feature it is only $10 more a month.' That sounded pretty good and the she said 'but wait. if you add this other feature it is only $7 more a month.' What is I had only paid attention to the Marginal Cost and not asked what the Total Cost would be?