It's hard to get worked up over Mayor Bloomberg's fight to ban big sodas from the city streets. The sheer entertainment value of his anxious municipal parenting more than compensates for any angst over the encroaching nanny state. But amid all the chatter, one important aspect has been overlooked: The super-size soda is probably the best source of cheap calories known to man. Even in New York, a couple bucks can buy 40 ounces of fizz—which works out to more than 500 calories per dollar.

How did they fit all those calories into that little box? It was a sort of caloric clown car. Rob Shepperson

Don't think this isn't a consideration for some people. In what may be my all-time favorite study, a bunch of NYU researchers spent two weeks collecting receipts from fast-food patrons around the city to see how many calories folks were buying per meal. A month later, after the City Council passed a law requiring chains to post calorie counts on their menus, the researchers returned to collect more data. Aha! After the calorie counts were posted, the average calories purchased per meal actually rose—to 846 from 825. My conclusion: Some folks were trying to buy as many calories as they could afford.

This was no fluke. The same phenomenon was found in a larger study by RAND and the Department of Health covering 11 different chain restaurants across the city. It also discovered that patrons in poor neighborhoods consistently bought more calories than those in wealthier areas.

So if the big-soda ban goes into effect, what are the alternatives for the New Yorker in search of cheap calories? According to the RAND study, the chain where patrons bought the most calories per meal was Domino's—an impressive 1,029 per visit, compared to 868 at KFC and a paltry 475 at that hangout for sissies, Au Bon Pain. It seemed like a good place to start.

I opted for the 1,400-calorie Chicken Alfredo BreadBowl Pasta. Believe it or not, this is a heaping portion of penne served in giant bowl made out of bread. You're supposed to eat the bowl. If you wanted, I suppose, you could just keep going and eat the cardboard box.

It's quite a creation. The eight-inch bowl was pillowy, chewy and crusted with parmesan as yellow as the sun in a picture book. Alas, it's on the pricey side: At $7, the meal works out to roughly 200 calories a buck. Hardly a deal.

An editor suggested Popeyes, the Louisiana fried everything chain. Here I had more luck. The special advertised in the window—910 calories' worth of wing, thigh, leg and biscuit—cost just $3.79. I could only marvel: How did they fit all those calories into that cute little box? It was a sort of caloric clown car. We were headed in the right direction.

The homeless seemed like an obvious source of inspiration, since they need to be tight with their food buck. I asked around. Marion Nestle, the famed NYU nutritionist, said she knows one homeless guy hanging around campus who bums a dollar off the security guards and spends it on a coffee loaded with 16 sugars.

This sounds very clever, but 16 packets of sugar contain just 240 calories. In fact, as it turns out, the homeless tend to make lousy food choices all around. Don't tell Papa Bloomberg, but researchers say their diets tend to be high in cholesterol and saturated fat, and they have horrible lipid profiles.

The one angle the homeless have figured out is the doughnut factor. Vagrants eat a lot of doughnuts, researchers say, and for good reason. A dozen from Dunkin' Donuts on the Lower East Side costs just $7.89, and if you get the highest-calorie variety—the chain's chocolate coconut cake doughnut—we're talking 836 calories per dollar.

Alas, the chance that any given Dunkin' location has the chocolate coconut cake variety in stock is slim (believe me, I tried). And 12 doughnuts is too many at once. Even if you eat one at every meal, the box will last four days, and who wants a four-day-old donut?

A better breakfast choice is Red Hook's IKEA. As the in-store posters advertise in a disturbingly large font, the store's 99-cent breakfast (scrambled eggs, potatoes, bacon) packs a generous "365 CAL." And on Mondays, breakfast is free.

As for the mom-n-pop options, the obvious contenders turn out to be surprisingly weak performers. The special at 99¢ Fresh Pizza ($2.75 for two slices and a can of soda) works out to just 270 calories per dollar. And the recession hot-dog deal at Gray's Papaya fares even worse.

Thank God for Chinatown. The $3 special at Wah Fung No. 1 Fast Food on Chrystie Street features a mad butcher in a juice-spattered apron wielding a giant cleaver. Place your order (choice of roast pork or chicken) and he'll grab a fatty glazed carcass from the steam table, hack it into pieces—watch out for flying meat!—and heap it atop a mountain of rice with a side of sautéed veggies and a big ladle of murky who-knows-what. The meal is insanely delicious, as roast pork tends to be, and by my estimate packs 1,100 calories, making it a better caloric deal than Popeyes.

Still, we can't always be in Chinatown when hunger strikes. It suddenly occurred to me that the real answer was lying in wait on nearly every street corner—the bodega breakfast special. Your standard $1 bagel easily packs 700 calories when topped with a generous cream cheese schmear, and will sit in your stomach all day long, like a chicken inside a python.

Don't worry, you'll walk it off—on your hike out to Jersey for a super-size soda.

—Ms. Kadet, who writes the "Tough Customer" column for SmartMoney magazine, can be reached at anne.kadet@dowjones.com