It's an integrated textbook series in elementary Japanese which is utilized college, high schools over the world. Develops the skill of speaking, listening, reading and writing. Effectively to learn!
Two volumes, 23 lessons approx. 300 kanji, 1100 vocabulary. Estimated 200 hours to complete.
Official site: http://genki.japantimes.co.jp/index_en
Here you can buy GENKI series direct fromAmazon Japan to save your money.
But maybe not needed because it's easy to do.