It's my understanding that coffee grounds can be mixed into bioactive soil as natural fertilizer. It's reasonably common for gardens. For that usage, it's only a very small percentage of coffee in the dirt and sand mixture. In that situation, it's very unlikely to be unsafe.

I currently buy the compressed bricks of coco fiber from amazon which aren't too bad expense wise, but someone else might have better suggestions on what kind of inexpensive, natural looking options there are for you to consider.