True, there are many other costs associated with the line; for brevity's sake I cut it short. However, to illustrate the cost to manufacture fly lines, Cortland is able to sell their "Fairplay" fly lines to Walmart for such a low price that Walmart can then profitably market the lines for $12.96. Assuming an average Walmart retail markup for this type of goods of 33%, Cortland would be profitably selling the lines for $8.64. Assuming Cortland also makes 33% over cost-to-manufacture, the cost-to-manufacture would be $5.76. ("Fairplay" lines are three feet shorter than the "Cortland 333+", but the same basic materials and manufacturing methods go into both.)
But, as I said earlier,
IMO, whatever line feels best on the rod with the way you cast to the average distance you need... is the line you should buy, regardless of price.