For $3 I bought a little brush thing that I screwed to the wall and my cat can rub and scratch himself on it to his little heart's content.

ETA, the one I bought is currently unavailable but it was this one: https://smile.amazon.com/gp/product/B07CV7TF5D/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1