I think one Iruka fragment is about 40 coupons/ingots if I remember properly. I am not entirely sure. So here are the estimate prices. Please note that these prices could be completely different than what you see as I could be overestimating.

10%: 36

20%: 32

30%: 28

40%: 24

50%: 20

Just multiple the discount price by the number of fragments you need and you should get the full estimate price.

The 50% tag on a ninja is mostly hypothetical as I have seen the 50% tag once or twice on a few non-ninja things. I think there is very very very slim chance it could be paired with a ninja. I have also seen 40% once or twice on a ninja. 30% and 20% discounts on ninjas are the most common for me though.