It looks like some kind of agate. I cannot tell you what it would be worth but if anyone were to venture a guess they would need a size reference and maybe better pics. Knowing where it is from could also help.
For price range, take it to a local rock shop. Geodes such as yours are fairly common. Color, banding, size, texture. All these and more can affect price. Demand is the most important factor, and can easily outweigh all other factors combined.