Try the Aldi in on Front & Oregon is South Philly. The 57 bus takes you to within a few blocks (4th & Shunk or 4th Oregon about the same distance from the store) and you pick it up to go back north on 2nd & Oregon.

Alternatively, you can take the 57 all the way to Whitman Plaza and go to the Shoprite. More expensive than Aldi, but cheaper than Acme.