GiveDirectly (https://www.givedirectly.org/) gives 88% of the money straight to recipients and offers a nice baseline for charity work.

There's also better metrics than "how much money does the charity take off the top" which you can learn about in Will McAskill's book "Doing Good Better," namely you can try to track things like "how much good are we doing for the amount of money we get." The main idea is that if a charity can use more of its donation money in order to have a better impact, then that's what it should do.