I've gotten some cheap, under a buck, plants at the box store cause they were "dying". It just needs a bit of love and TLC. However, that won't always be the case.
And each box store handles things differently. At my ex's old home depot store, any broken bag of garden stuff was tossed on a pallet. Rocks, mulch, dirt, and a rare occasion ferterlizer. They'd sell the pallet for $5, and I'd just have them drop the pallet on the back end of the truck bed. Fit perfectly in the Ranger.
Some of it was good stuff, some of it not so great stuff. I'd take what I wanted and give the rest away on free cycle.
Now the home depot store I worked at in Orlando did no such thing. Like it was a crime against humanity. So you just have to talk to the department head and see how they mark things down.
As far as plants go, each store orders locally from different nurseries. And some of my favorite nurseries in South Florida, weren't in Orlando. Although there are some nationwide nurseries, I think Bonnie is one of them. About half or more come from local nurseries.
I've bought most all of my vegetable plants this year from the flea market. Most of them were really cheap and a lot better than the box store. And around here there's nurseries a dime a dozen, but of course this is almost all agriculture out here.