There are, however, other costs which may include:
+if a person lives in a rural area what direct costs are involved in travelling to/from a destination with a supermarket? i.e. fares, car fuel, car parking, and the extra pollution produced by those cars etc?
+How much time is spent in travelling?
+Is the gf product(s) you want always available?
+are you limited to just one brand? Or is there a choice?
+Is there a choice of products using different ingredients? eg (for those who can tolerate it) gf products made with Codex wheat starch?
+Given that most shoppers of gluten free products are not coeliacs are supermarkets committed to continue stocking gf if the current gluten free trend declines?