Dude if you don't have a job right now why would you put your savings on a browser game? o_O

As for your other question, cheapest events for power would be Lucky Board (random stuffs), Treasure of the Sage (refine runes, cave key packs, myouboku packs). For ninja frags it depends, Jounin Minato and Masked Man currently have a 40% discount in Treasure of the Sage. Mission Mobilization gives you a good amount of redeemable frags without even putting ingots on it. Fateful Choice rates depend on how lucky you are in the points it gives you.

But seriously dude, savings on a browser game? When you don't have a job currently? My advice, just get the monthly card and be content with that.