Ten Million Dollars or Ten Billion Yen in the original Japanese version is a motive used in Chapter 3 of Danganronpa: Trigger Happy Havoc offered to the students by Monokuma in an attempt to convince them to murder each other.
Monokuma offers Ten Million Dollars to the student who successfully graduates from Hope's Peak Academy via the rules of the Mutual Killing Game.
Chapter 3: A Next Generation Legend
After calling all of the students to the Gym, Monokuma declares that he will change his strategy to work with the students than against them. He then announces that the Blackened who "graduates" will receive ten million dollars, which Byakuya Togami states isn't nearly enough for him to consider a proper incentive. Kyoko Kirigiri mentions that money is a common basic incentive, but Aoi Asahina, Sakura Ogami and Makoto Naegi declare that no-one would kill for money. Monokuma brushes them off and leaves. Afterwards Toko Fukawa begins to panic and paranoid about everyone's money situation, until Sakura gets her to stop.
In the end, Celestia Ludenberg succumbs to her greed and comes up with a plan to win the money, stealing Alter Ego and telling Hifumi Yamada that Kiyotaka Ishimaru had done so, as the two were in a feud over it. After Hifumi killed Kiyotaka, Celeste killed Hifumi in turn. Her crime was found out during the Class Trial by a combination of Makoto, Byakuya and Kyoko working together to piece together her crime.
After Celeste was found guilty, before her execution, it was explained that she did this in order to fulfil her dream of owning a castle.
Chapter 6: Ultimate Pain, Ultimate Suffering, Ultimate Despair, Ultimate Execution, Ultimate Death
After Makoto deduced that the mastermind was Junko Enoshima, the latter challenged the survivors to guess the "themes" behind each of Monokuma's motives for murder. Makoto correctly deduced that the theme of the third motive - the ten million dollars - was "Greed". Junko later explained that each motive represented a "Seed of Despair", something that could drive people to do terrible things if the right pressure was applied. With the revelation of the world's state following The Tragedy, the money would likely have been completely useless even if the murderer had gotten away with their crime.