At first, he promised to give 100 million yen to people who retweeted at random. But, he finally gave it to people who retweeted their dream or would use it for charity.
people who retweeted their dream, or to those who said they would use it for charity
質問者様の文章で通じると思います♪
指摘するのであれば、この短い文章で唐突な finally が不自然かもしれません。
この場合は「最終的には」というニュアンスの “ended up” がいいのではないかと思います。
At first he promised to give 100 million yen to random followers who retweeted his tweet. But he ended up giving it to people who retweeted their dream, or to those who said they would use it for charity.
日本 
