Hand ground finely faceted bullseye agates in good shape are definitely valuable, though probably not as highly prized as they once were. I’ve seen 3/4” mint ones go from $15-20 and up depending on pattern, color, seller, and market whim. You need a loupe to see if yours is machine ground (totally smooth) or hand ground - if the latter, under 10X magnification you’ll see little facets in the surface. Unfortunately yours was well loved by someone and has a lot of moons and damage, probably negating any value it might have.