To find the price per ounce for each grocery store we have to divide the price by the size of the bottle:
Hawkin's Grocery:

$0.25 per ounce
MItchell's Store:

$0.32 per ounce
Selena's Market:

$0.30 per ounce
Teresa's Store:

$0.20 per ounce
We can see that Teresa's Store has the lowest price per ounce