You may pay nearly $8 for a McDonald's Big Mac in Massachusetts versus $3 in Oklahoma. Here's why costs can vary — even for locations across the street from one another.

• High inflation and commodity costs are forcing chains to raise menu prices.
• A New York college student created a searchable fast-food index to highlight prices in the US.

Riley Walz is a business major at the Macaulay Honors College at the City University of New York and dabbles in coding. The 20-year-old one day hopes to run his own business. Until that happens, he's taken on the unofficial position of "fast-food data scientist," thanks to his latest side project, the Fast Food Index.

Walz's index, distributed to classmates last month, tracks the pricing of four popular fast-food items: McDonald's Big Mac, Taco Bell's crunchy taco, Chipotle's chicken burrito, and Chick-fil-A's chicken sandwich. He created the searchable index last month after noticing his go-to chicken burrito from a Chipotle near Columbia University cost 15 cents more than his neighborhood Chipotle on the Upper East Side.

As a business student, he understands that cost of living plays a factor in menu pricing, but he wondered why prices of the same item would vary that much from one part of the city to another.

"I was interested to see where's the cheapest burrito in the entire country and where is the most expensive one," he told Insider.

Three weeks later, he had his answer.

According to the Fast Food Index, the most expensive Chipotle chicken burrito is sold for $11.10 in Manhattan's garment district. There's a three-way tie for the cheapest burrito in Iowa City, Iowa; Athens, Ohio; and Ann Arbor, Michigan.

To create the index, he wrote a script that scraped menu data from the apps of each chain.

"It just kept making a request, pretending it was going to make an order at every single store," he said of the script.

The index is searchable by Zip Code and highlights the average price of all four menu items in the US and the three cities where each item is the most and least expensive.

While it makes sense that New York is home to the most expensive Chipotle burrito, Walz's index uncovered some head-scratching geographical pricing. For example, two rest stops on opposite sides of the Massachusetts Turnpike both have a McDonald's. One location charges $6.19 for a Big Mac, while the one directly across the highway charges $7.29.

When asked about the $1.10 differential, as well as its overall pricing strategy, McDonald's told Insider that menu "prices are ultimately at the discretion of our franchisees and may vary by restaurant."

Other Fast Food Index findings:

• At $7.89, a McDonald's in Lee, Massachusetts, is home to the most expensive Big Mac. The cheapest can be found in Eufaula, Oklahoma, for $3.39.
• Generally, menu prices for restaurants close to college campuses are higher than nearby restaurants off campus, Walz said.
• In metro areas like New York or Los Angeles, prices can vary up to 30% from neighborhood to neighborhood, except Chick-fil-A, whose prices are usually pretty consistent, Walz said.
• Los Angeles, Washington, DC, and New York City are home to the most expensive Chick-fil-A chicken sandwiches, with prices ranging from $5.79 to $6.29.
• Whittier, California, and Ellisville, Mississippi, are tied for the cheapest Taco Bell crunchy taco, at $0.99. The most expensive crunchy taco sells for $3.39 in Lebec, California, a town of fewer than 1,500 people.

Taco Bell couldn't explain the expensive taco price in Lebec, saying that franchisees set their own prices with the "goal of providing our guests with incredible value."

Raising menu prices is becoming standard practice this year at chains like Chipotle and McDonald's. Earlier this year, McDonald's told investors that menu prices were up between 8% and 9% in the second quarter. Chipotle menu prices increased by 4% in August, and the company has raised prices for delivery. In the third quarter, delivery pricing at Chipotle increased by 13% compared to the same period last year.

The restaurant consultant Tim Powell said inflation might play a factor in higher menu prices, as many chains are passing off higher commodity costs to consumers. In October, money spent on food away from home, which includes restaurants, rose 8.6% over last year, according to the Consumer Price Index.

Powell, the managing principal at the industry consultancy Foodservice IP in Chicago, said menu prices are primarily influenced by the cost of doing business in a specific city or state, where labor and real-estate costs vary.

"California and New York have very high labor and real-estate costs," he said. "Each franchisee may charge a different price based on the cost of labor or food or real estate."

That's true for McDonald's, Taco Bell, and Chick-fil-A, the companies told Insider. Chipotle, which owns and operates all its restaurants, didn't return a request for comment.

Walz's index helps illustrate how cost-of-living factors trickle down to the consumer, but the index is not foolproof.

"I'm like 99.9% sure I have everything, but it's definitely possible I missed something," Walz said.

His script scraped pricing from 13,273 McDonald's locations, 2,495 Chick-fil-A locations, 7,414 Taco Bell restaurants, and 3,083 Chipotles. But those store counts differ slightly from chain totals, according to research by Insider.

Either way, Walz said he set out to confirm if New York City was home to the most expensive Chipotle burrito — and it was. Plus, he said, the coding challenge "was actually kind of fun."

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