If you feel you low on money now wait until they implement blooming. Without the occasion coin boost event like on DMM were are all going to be out of coin fast.
Just blooming costs a lot, then you get to level the unit from LV. 1 a third time.

I have 4.9 million coin right now, it will vanish when blooming shows up.
I keep making coin because I can't get manju faster than I get coin.