If the person is indigent, they should be eligible for Medicaid if it is a medical issue or needs some form of medical inpatient care.
Residential is different from inpatient. Residential is typically for maintenance, while inpatient is for acute care.
in NYS OPWDD or OMH may have funding.
There are too many details missing here.
Perhaps Pesach Tikvah in Williamsburg may be a source of help.
ZD, FYI, there are baalei tzedakah who do provide such amounts.
However, there may be programs to pay for the treatments or hospitalization under regular or waivered programs.