A few years ago, I was very diligently tracking _all_ my family's grocery purchases. I kept every receipt, entered it into a spreadsheet, added categories (eg, dairy, meat), and calculated a normalized cost per unit (eg, $/gallon for milk, $/dozen eggs).
I learned a lot from that, and I think I saved our family a decent amount of money, but man it was a lot of work.
@mynameisash I'm curious what you learned... maybe I can help more people learn that using Popgot data.
I just dusted off my spreadsheet, and it's not as complete as I'd like it to be. I didn't normalize everything but did have many of the staples like milk and eggs normalized; some products had multiple units (eg, "bananas - each" vs "bananas - pound"); and a lot of my comparisons were done based on the store (eg, I was often comparing "Potatoes - 20#" at Costco but "Potatoes - 5#" at Target over time).
Anyway, Costco didn't always win, but in my experience, they frequently did -- $5 peanut butter @ Costco vs $7.74 @ Target based on whatever size and brand I got, which is interesting because Costco doesn't have "generic" PB, whereas Target has much cheaper Market Pantry, and I tried to opt for that.
Our main example is something like pasta. Our local grocery stores all carry their own brand of dirt cheap pasta but it’s not as good as the more expensive pasta at Costco. Comparable pasta at the local grocer would be more expensive.
For items that are carried at both stores, Costco is usually no cheaper than the regular retail price and rarely much more expensive.
We have historical price tracking in the database, but haven't exposed it as a product yet. What do you have in mind / what would you use it for?