It’s a website that lets you sort amazon by price per ounce/pound/count
Some examples are:
Cheapest rice per pound https://bangyourbuck.com/search/rice/Lb/US/grid
Cheapest batteries by count: https://bangyourbuck.com/search/aa batteries/Count/US/grid
Hard drives by terabyte: https://bangyourbuck.com/search/hard drive/Terabyte/US/grid
Been using it for months, and I can’t stand using Amazon without it now.
For the comparison I was doing (it can be hard to compare the two products,) I found paper towels were almost always cheaper (per unit area.)
But that was pre-pandemic, so prices are probably way different by now.