About Sumi Ink
Sumi Ink stick is called just Sumi in Japanese. It’s made of oil based soot or pine based soot.
Prices vary depending on the materials and if it is aged. For beginner to intermediate learners, you can find good enough Sumi in the price range between US$5 to US$15. (as of 2019)
There are some Blue-ish colored Sumi, but you should have a standard black one for regular practice.