According to the weekly Kroger ad for their store in north Fort Worth (Texas), a can of Simply Organic beans (very tasty beans, I should add) is $1 with a Kroger card; the same goes for a can of Hormel chili (no beans in chili, please). My back-of-the-mousepad calculations say that approximately 37 regular cans will fit in a 55-gallon drum, the kind usually used for these food drives. That means that, in a regular 8-story office building with two deposit locations per floor, filling all of them to the brim will cost $592. If you go the other way and just put three cans in the areas visible to the public, that's $111 to make a small but visible impact.
Yep, it's advertising and showmanship, but that food also does go to people who will actually use it, so it has the benefit of doing a little bit of good, unlike most advertising.