My calculations say ~1847 coupons per frag. So, To get 3* you would need ~148k coupons. With 148k coupons you could buy ~1200 seal scrolls and get him 3* from GNW treasure. This might be how they came at the price for his frags.

Now for 4* once you have him 3*, this will cost ~185k coupons. Which probably would be cheaper than trying to get him 5 more times from GNW treasure. But, come on. Unless Enfeeble does something gamebreaking, I don't see the point. A couple years ago the most expensive coupon frags were Naruto 9tails chakra for 700, and that is kinda where I expected the price to be, which would have been ~105 coins.

Top 10 most expensive average coupon price ninja

1) Madara Founder - 1847

2) Naruto 9tails Chakra - 573

3) Ay 4th Raikage - 469

4) Sasuke Susano'o - 447

5) Tsunade 5th Hokage - 391

6) Madara GNW - 300

7) Kakashi Susano'o - 293

8) Ay 3rd Raikage - 280

9) Kabuto Sage - 278

10) Sasuke Rinne - 275