Kome koji is usually prepared by adding commercially-purchased koji-kin to steamed rice and allowing it to grow. Is it possible to propagate the koji-kin by adding kome koji to steamed rice, allowing one to spend less money on koji-kin?
I just educated myself on this, and I found a description of the sake making process ( http://www.taylor-madeak.org/index.php/2008/10/17/growing-koji-for-homebrewing-sake?page=2 ).
They explicitly state that you can store the culture for next use. What they don't say is how fragile this culture is. But it sounds quite stable, so I guess you have to buy it the first time, but then you can reuse until it stops working.