You forgot to calculate in the price of bicycle fuel!

I get 12 packs of Cliff Bars from Wegman's for $10.99/box, and wind up eating part of one before I leave work, and finishing it on the commute home. I also use Elixir or Nuun. 6 tablets of Nuun in a 3L CamelBak or 4 tablets of Elixir. For an 8.5 mile commute I down about 1L. My maximum consumption per months, 20 days commuting, is about $18.33 in Clif bars + $28.15 in Nuun ($16.89 for a 4 pack of tubes of 12 tablets each). That's $46.48.

For reference, the car commute is 7.7 miles each way at 23mpg, $52.09 of fuel, for a savings of $5.49/mo.

Mind you, those electrolite tablets are expensive. Powdered Gatorade is much cheaper, but sugary and nasties up the CamelBak. As compensation, though, I tend to gulp down Gatorade before I leave (about 16 ounces), and even bring a water bottle containing Gatorade or Tang. Clif bars are also expensive versus food; it's much more cost-efficient to bring a bit extra lunch and save it until I leave to mitigate the daily commute need for a Clif bar.

Clif bars are something I would use on a 16 mile trip if I got hungry during it; more likely I'd eat lunch before leaving, or eat something and pack lunch. For a 48 mile grocery shopping spree all around town that'll take me 4 hours, I'd probably bring a Clif bar, because lunch will not likely cut it when we're talking about 4 hours of near-continuous cycling.

Amusingly, good planning can evade the need for using your Clif Bar supplies, even though they're incredibly tasty. A little playing with water bottles and powdered sugary sports drink can dodge the need for expensive electrolyte tablets, too; not like anyone makes a non-sugar powder.