Use rest from the deodorant
I have a glass deodorant. My daughter wanted to have the bullet for crafting.
When I thought he was empty, my husband made the bullet out of me. We noticed that there was still a lot in it.
I took these with a spatula and applied them with my fingers. You could probably also a brush o.ä. use. This rest has been enough for a few weeks with daily use.
With toothpaste or something, I always do it so that I cut it open. But at the Deo I had not come up with the idea so far. I do not know if that goes with every Deoroller. With a Deoroller for 50 cents that will probably not be profitable. But at an expensive, you can already save something.