Clay,
I’ve used a soft plastic bass lure called a Zoom super fluke to practice casting with my kid. It’s heavy enough to cast longer distances without any added weight. Just attach it to the mono with a couple of over hand knots. They’re surprisingly durable for soft plastics, can be found pretty much anywhere lures are sold, and are cheap. Plus it’s a real lure(minus a hook) that kinda looks like a fish…can make casting to targets in the yard a little more fun.
Matt