I only have an Aldi near me. Costco is in another city across the bridge and I've not been to either one.
These Are the 7 Cheapest Grocery Stores in the U.S.1. ALDI
Value for money: 90% of survey respondents said ALDI offers value for your money.
Locations: 2,300 stores across 39 states ..........
2. Woodman's Markets
Value for money: 88% of survey respondents said Woodman's Markets offers value for your money.
Locations: 19 stores across two states...........
3. WinCo Foods
Value for money: 87% of survey respondents said WinCo offers value for your money.
Locations: 139 stores in 10 states...........
4. Lidl
Value for money: 83% of survey respondents said Lidl offers value for your money.
Locations: 181 stores in 10 East Coast states ............
5. Market Basket
Value for money: 81% of survey respondents said Market Basket offers value for your money.
Locations: 93 stores across four East Coast states............
6. Grocery Outlet
Value for money: 78% of survey respondents said Grocery Outlet offers value for your money.
Locations: 457 stores across eight states..........
7. Costco
Value for money: 75% of survey respondents said Costco offers value for your money.
Locations: 594 across the U.S.............
https://money.usnews.com/money/personal-finance/spending/articles/these-are-the-cheapest-grocery-stores