You don't need 50k bp for this exam. I did it with 43k~ bp but I did it as wind main. Maybe try it with:

Mei - Sage Naruto - X
Water Main - Ao - X
X - X - X

Talents: 3,2,1,1,2
Summon: Gamaken or Gamachu

I used:

Sage Naruto - Wind Main - Gaara Kage
X - Iruka - X
X - (Naruto clone) - X

Talents: 3,4,2,3,3
Summon: Katsuyu

It's some time ago I did it. But if I remember correctly the firemain has to be blinded in round 1 and kill lightning main and fire main in turn 2. Some players go for earth main next, I went for the wind main since Impetus is more anoying. I killed the water main last since she's the least dangerous in this exam.

So in turn 1 blind fire main and use iruka to interupt him.
Turn 2 should go on fire main again with sage naruto and use impetus to reset skills. If you reset skills before your naruto mystery goes off, it still resets. Use Iruka to interupt Windmain.
After turn 2 it's pretty much done.

You could try to chaos all of them in turn 2 with shark mystery and place water main in first position. The chance that you can pass any exam with this strat is very low because you really need to be lucky on your crits.