By which I mean "free."
You HAVE insoles in your shoes, right? Like, they came with the shoes. So you can pull them out and they're made of crappy foam, right?
You can go to Walmart / Amazon whatev and buy some "better" insoles but they will also be made of crappy foam, unless you spend a lot. Some of them are laughably bad.
Anyone here cut new insoles out of anything around the house to maybe just get a bit more life out of an old, possibly backup. pair of shoes? Your podiatrist won't approve, but can't be much worse than the shitty ones they sell at the store.
Materials that come to mind: some sort of packing foam, scraps of commercial carpet. The internet recommends cheap yoga mats and sheets of cork, but that's back to buying things unless you have a really weird assortment of scrap materials at home. I'd also think a couple sheets of heavy corrugated cardboard if you're just extending the life of the shoe for a bit.