(NEXSTAR) – The most expensive Big Macs in the country are more than double the price of the cheapest, according to an online resource created by a tech-savvy McDonald’s customer.

Sacha Fournier, a marketing executive from the U.K., developed McCheapest.com to track Big Mac prices across the U.S. after purchasing a few of the signature sandwiches in the NYC area and becoming astonished by the price differences.

“I thought to myself, if the price varies this much between two stores, how much does it differ across the entire U.S.?” Fourier told Nexstar.

Fournier, a former data analyst who dabbles in coding, soon began working on a program to answer that very question. But he quickly learned that McDonald’s doesn’t display menu prices for individual restaurants on its website, so he built a custom scraping tool that connects to the McDonald’s app. It runs 24 hours per day, continuously adding Big Macs to the app’s cart (to determine the pre-tax price) and displaying the results on a map at McCheapest.com.

As of Wednesday morning, the most expensive Big Mac in the United States, at $8.09, is selling at a highway rest stop in Lee, Massachusetts, according to McCheapest’s latest data. The least expensive, at $3.49, can be found in Stigler, Oklahoma.

“I wasn’t expecting to see such a staggering variation in prices,” Fournier said. He also noted that the McDonald’s in Lee is situated a mere 400 feet across the highway from another rest-stop McDonald’s, where Big Macs are selling for only $6.69 each.

Prices appear to change somewhat frequently, too. When Fournier launched McCheapest on Feb. 10, the most expensive Big Mac was selling at the same Lee location for $7.89. Across the street, they were only $6.39 apiece.

McDonald’s could not corroborate the accuracy of McCheapest.com. The prices on Fournier’s site, however, appear to align with Big Mac prices as displayed in the McDonald’s app, though Fournier indicated on Reddit that there is a lag when it comes to real-time pricing changes at each local McDonald’s.

His site also doesn’t take into account any bundle-based deals or in-app promotions, which might allow a customer to score a Big Mac for less than its displayed standalone price (e.g., a two-for-one deal, a meal deal, etc.).

Nevertheless, Reddit users are reacting to McCheapest with a mixture of awe and appreciation.

“This is eye-opening,” wrote one user, while another claimed he’d be checking McCheapest “on a daily basis” for his nearest, most affordable Big Mac. Others also began speculating why Big Mac prices were wildly different, theorizing it may have something to do with local rents, labor rates or costs of living.

A representative for McDonald’s would only confirm that pricing is “determined at the restaurant-level by franchisees and may vary based on location.”

Inflation, meanwhile, has only driven the price of fast food higher. Between March 2021 and March 2022, the National Restaurant Association determined that fast food prices rose 7% due to increased food and labor costs. And over the past 10 years, the price of a Big Mac has increased by around 40%, according to the Economist’s Big Mac Index, which was created to measure the American dollar’s buying power when compared to other currencies.

Fournier, taking inspiration from the Economist, also plans to add a data page to McCheapest with state- and local-level charts, allowing for “further analysis.”

In the meantime, he might start tracking the fluctuating prices of other common foods. Folks on Reddit have already suggested eggs, Burger King Whoppers, or other McDonald’s favorites including hash browns or McChicken sandwiches.

“I do love a good McDonald’s,” Fournier told Nexstar of his possible future plans. “I might have to add nuggets to the site soon.”