As our calculator shows, the perhaps impulsive addition of just one service to your budget can snowball into a hefty outlay over a hypothetical half-century horizon, particularly when you're looking at that "true" lifetime cost. Take someone paying for Netflix's NFLX, +0.07% standard subscription and Hulu, with no add-ons. That person is looking at a monthly bill of $18.98, and a lifetime aggregate cost of $19,264. Factor in the opportunity cost -- as represented by how much money could have been made investing that same money in the S&P 500 over those years -- and the lifetime cost balloons to...