You get 30*25 = 850 a month from daily quests. Then you get 8*4 = 32 konans for finishing last place in leaderboards. Then you get about 200 kobans a month for doing the 22 Koban rewarding event quests. Then you can get more kobans from contests and leagues (if you don't get, say 100 kobans a month from these, you are doing things very wrong).

This is enough kobans to buy a 900 pachinko * 10 spin every month and still have a surplus, or it is more than enough to top off any event boss girls that you didn't get due to RNG and develop a large koban surplus for Epic Days (girls cost 600 kobans each on average if you are doing refills) or legendary days (900 on average).

I much prefer that system to system where I can spend kobans and get nothing due to rng, not even shitty boosters.