What you have here is a KR-3. They came in 2 sizes. 2" and 3". They come in 4 colors. Cobalt, Cornflower, Amber and Clear. I have never seen them in any other color than Cobalt and only a picture of a clear one. Poisons4me was right on in the price range. You can expect to pay more towards the upper end for the larger one and/or if they have their dobber included.
The clear and amber issues are the most rare and are worth over $800. I would also guess to pay more for the cornflower as well as they are hardly ever seen. Nice find!