Heavenly Madeleines

We have recently discovered the angelical taste of Madeleine cookies, especially when consumed with a cup of morning coffee. And we quickly became Madeleine junkies. In fact, busy as we are with work and kids, we find ourselves driving all the way to Costco to snap a box of heavenly Madeleines.

I know very well that we are not alone.
French novelists, Marcel Proust, wrote hundred years ago in Remembrance of Things Past:

She sent out for one of those short, plump little cakes called petites madeleines, which look as though they had been moulded in the fluted scallop of a pilgrim's shell. And soon, mechanically, weary after a dull day with the prospect of a depressing morrow, I raised to my lips a spoonful of the tea in which I had soaked a morsel of the cake. No sooner had the warm liquid, and the crumbs with it, touched my palate than a shudder ran through my whole body, and I stopped, intent upon the extraordinary changes that were taking place…at once the vicissitudes of life had become indifferent to me, its disasters innocuous, its brevity illusory…

Alert to the shell-like shape of the cookies, I recently discovered that they are also sold by our local supermarket: a box of 10oz is $4.99. Costco is way cheaper: a large box of 21oz is $5.99, but the store is 20mins away. I would say that I value the time and gas spent on driving to Costco as $50 more that driving and shopping at the local store. How many Madeline boxes do I need to buy at Costco to make a trip there more cost effective than a quick stop at the local supermarket?

Enter your answer on our Family Puzzle Marathon page. Solve three and get a prize!