I've done the bring from home math vs. the eat out. Seems like a lot of people discount the fact that food brought from home cost $$ too. I find on a $6 eat out, I pay about $3 to replicate from home.
Now, if you are eating a few carrot sticks and a piece of cheese I understand. Curious about the comparison...
I can (and usually do) eat for less than a dollar. I try to stay stocked in frozen leftovers to avoid processed food. My most recent example is chicken stir fry and grilled asparagus over rice that cost about $10 in total and produced 7 servings, for a per-meal price of $1.42. My regular standby, tricolor rotini or penne ($1) in marinara ($1) with a small amount of turkey sausage ($2) and various veggies ($2-3) is even cheaper per serving. As backup, I stash store-brand soups and Spaghettio knockoffs that run from $0.69 to $0.99, or occasionally Cup-o-Noodles ($0.50). High in salt but OK for occasional use.
$6 is the low end for our cafe'; the full meal deal is $9. Take that over 2,500 workdays + a decade of investment returns and there you go.
I still buy breakfast occasionally, since I can get a pretty decent protein dose (eggs+bacon/sausage) for under $3, but I'm sticking more to oatmeal and frozen turkey sausage lately to keep the per-meal cost at $0.20-$0.40.