Another factor in price is that the individual squares are considered a “convenience” product, and so they’re more expensive for no good reason than the roll. Just get the roll; it’s not that hard to tear off a sheet, and you can even pull off a shorter or longer sheet if you need to.
Ok, so I got 3.2g vs 3.0g in my test. (Sheet of aluminum cut to the exact same shape by being stacked on top of each other and trimmed to about 9.5"x8.25") This is Reynolds Heavy Duty vs Best Choice heavy duty. So not as much a difference as I had expected.
I don’t see anything especially unusual about aluminum foil prices but it’s not something I pay especially close attention to. But 100 ft of store-brand foil is currently $5.99, 25 ft is $2.49, and a whopping 200 meters (656 ft) is $20.99, which all seem perfectly reasonable. I did notice that name brands are much more expensive; 100 ft of Alcan is $8.99.
I looked at the Walmart website and compared the prices of Reynolds foil versus their Great Value house brand, and the price in cents per square foot was comparable, $0.04 to $0.11. The wide rolls and the heavy duty stuff was more expensive.