I agree with OP. 300 cave keys is pretty steep. I had to use coupons to make up for the lack of seal scrolls for the x10 draws. You would need 60K moon coins in order to get 300 cave keys. 50 cave keys is 560 coupons in the Cave Exploration menu. Of course saving always helps, but recommending over and over that people save instead of making the game such a way that you earn with immediate interaction just makes the game end up being one that's just hoarding fake materials for a pay-off you may never cash in on. People out here with hundreds of thousands of moon coins and coupons...for what end?

I would've accepted 200 cave keys at the very most.