I think the problem is that the antitrust ship has already sailed.

I don't think a government run grocery store would be looking to compete on the open market. It would be more along the lines of subsidized food for lower income households on food stamps, practically speaking. That is much more sutainable than one that's open to the general public.

If a government run grocery store could provide a fair price for items we are currently being gouged on, I doubt they would be able to keep up with consumer demand. Essentially middle class and above will have to keep putting up with commercial prices.