Hey, Toshiro! Have you checked out the Asakusabashi area? Last time I went there on my way to Sensoji, I passed by several crystal shops right under the train station. You can’t miss them as they have huge crystals displayed in their windows (massive amethyst geodes!). However, I’m not so sure about their prices as I didn’t have time to actually go in and browse. But maybe you can drop by and see for yourself? Good luck!