According to the United Nations: "It is estimated that the additional cost of achieving and maintaining universal access to basic education for all, basic health care for all, reproductive health care for all women, adequate food for all and safe water and sanitation for all is roughly US $40 billion a year . . . This is less than 4% of the combined wealth of the 225 richest people." (UN Human Development Report, 1997.)
This is just conjecture, but that's probably pure cost of services and not cost assuming you need to build hospitals, schools, transport food and water etc.