Casual Gainer:
I would check out what's available locally e.g. smaller chains/independents and sign up to delivery apps for the occasional offer.
Munchies:
Unfortunately, depending on where you live, shopping at smaller/local chains are not cheaper. Often times, bigger chain stores will charge significantly lower prices as a way to undercut the competition in small towns or rural areas.
Nofbar:
Much of that price difference is because the bigger retailers get discounts for buying large quantities.
That is part of it, yes. But talk to anyone that lives or has lived in a very small town. When a chain store comes to town, they'll sell things at a loss for a time until the mom-and-pop stores can't compete and then close down.
Eventually, that store will be the only one available in the area. And if it closes down one day (which has happened in some rural areas), it will devastate everyone.
So yeah, shopping locally is very important for the economy. Unfortunately, it's not always the most cost-effective option.