Nonprofit organizations lack market feedback. Waste is a serious problem. Cause prioritization can help.
The lack of price feedback, or any feedback, for charities, would lead one to believe they may be the most inefficient organizations in the world, as they are not pressured to discover efficiency. The act of measuring their outcomes , as is done by GiveWell and other EA orgs are an important signal, but they cannot evaluate all charities.
We leads me to consider another way of providing feedback for organizations. If the people that the organizations themselves help can rate the help/effectiveness of the charity this can act as a signal. I'm sure many charities already do this, but making this information public, on some large social website designed to track all these reviews, can help add transparency to donors who then might allocate their resources separately, encouraging efficiency in charity orgs.
Now this idea presents practical problems. Many who these charities might be designed to help may have barriers to providing such info, such as no access to electricity, internet, being illiterate, or just plainly not being in a position to evaluate how much good a charity has done for them. A review of bed nets for malaria from the point of view of recipients may be lackluster as their benefit may not be seen or felt, after all.
So really charity evaluation seems like the best option, as EA orgs have come to.