UNHRC, among others. See my previous post.
Some country(s) would have to pay UNHCR or UNRWA. They don’t have mountains of discretionary funds.
In the past, The UN has been used to keep Palestinians from emigrating, so they remained as a weapon against Israel. If things have changed enough for this to work, it would be huge. There would still need to be a mountain of money from somewhere to buy out a million people (or two).
Dispersing them would likely be a key - nations that took in large Palestinian refugee populations before - Lebanon, Syria, Jordan - had painful experiences.