If Haiti were any other country in this hemisphere, a human-created disaster of this proportion would be a big international scandal and everyone would know about it. Not to mention the institution responsible for inflicting this damage – in this case, the UN – would be held accountable. At the very least, they would have to get rid of the epidemic.
In this case, getting rid of the epidemic could be easily accomplished. Cholera is transmitted mainly through drinking water that is contaminated by the deadly bacteria. To get rid of it, you need to create an infrastructure where people have clean drinking water and adequate sanitation. The Pan American Health Organization estimates that this would cost about $1bn for Haiti. In fact, that is close to what the UN has been spending in just one year to keep its 10,000 troops in the country.
Furthermore, these troops have no legitimate mission in Haiti. They are not "peacekeeping" troops, as they are often inaccurately described. There is no peace agreement for them to enforce, nor is there a post-conflict situation that would justify their presence.
In fact, the UN troops were brought into Haiti in 2004, after Haiti's democratically-elected government was overthrown by a coup that the United States and its allies helped organize. Their stay in Haiti has been marred by a series of scandals and abuses, including the killing of civilians, and a number of prominent cases of rape and sexual abuse of Haitians. According to polling data, most Haitians do not want them there.
So, there is one obvious source of money for ridding the country of cholera, but there is also plenty of money that governments pledged after the earthquake that has not been distributed. Only about 53% of the $5.35bn pledged by international donors has been delivered.
For the US government, it is just 27% (pdf), or $250m, of $900m pledged. If these governments want to help the UN fix the mess that they created, they have already committed the funds to do so.
And why shouldn't they pay? It wasn't the Haitian people that invited these troops to Haiti in the first place – it was the "international community".