i don't think the final boss have 25mio HP unless there will be another huge gap between the HP of the further bosses...
RB lvl 1: 50,000 HP // 50 SH
RB lvl 2: 150,000 HP // 150 SH
RB lvl 3: 300,000 HP // 300 SH
RB lvl 4: 500,000 HP // 500 SH
RB lvl 5: 750,000 HP // 750 SH
RB lvl 6: 1,000,000 HP // 1000 SH
RB lvl 7: 1,500,000 HP // 1500 SH
RB lvl 8: 2,000,000 HP // 2000 SH
RB lvl 9: 2,500,000 HP // 2500 SH
RB lvl 10: 2,750,000 HP // 2750 SH
RB lvl 11: 3,000,000 HP // 3000 SH
RB lvl 12: 3,250,000 HP // 3250 SH
RB lvl 13: 3,500,000 HP // 3500 SH
RB lvl 14: 5,000,000 HP // 5000 SH
RB lvl 15: 6,000,000, HP // 6000 SH
RB lvl 16: 6,125,000, HP // 6125 SH
RB lvl 17: 6,250,000, HP // 6250 SH
RB lvl 18: 6,375,000, HP // 6375 SH
RB lvl 19: 6,500,000, HP // 6500 SH
RB lvl 20: 6,625,000, HP // 6625 SH
RB lvl 21: 6,750,000, HP // 6750 SH
RB lvl 22: 6,875,000, HP // 6875 SH
RB lvl 23: 7,000,000, HP // 7000 SH
RB lvl 24:
RB lvl 25:
...
RB lvl 30: 25,000,000 HP // 25000 SH
i hope they restock the shop today, they could even add a zero at the end of every price, i wouldn't care XD
you would need around 98k sweat hearts, so no problem to clear the shop again^^