We develop an integrated model for estimating the internal cost of abyssal seafloor waste isolation. The model captures the major economic, engineering, geographic and social factors that influence the management cost for sewage sludge and municipal incinerator ash. Considering five representative metropolitan areas and five proposed abyssal study sites, we apply this model to produce cost estimates for four deep-ocean waste delivery system concepts. The results show that the unit cost depends primarily on regional waste volume, the marine delivery system and transportation distance. Based on available data, the abyssal ocean option may be competitive with present land-based disposal costs in New York City. The option is less competitive in other metropolitan areas.