Next-generation cholera and typhoid vaccines have the potential to reduce the burden of both diseases in areas where they are endemic. We examine the case for public investments in these vaccines for the Tiljala neighborhood of Kolkata, a low-income, high-incidence slum. We take a social perspective and use three measures of the vaccines' economic benefits: avoided private and public costs of illness (COI); avoided COI plus mortality risk reduction benefits; and private willingness-to-pay (WTP) derived from stated preference studies we conducted in Tiljala in 2004. The study represents a unique opportunity to evaluate vaccine programs with a wealth of new high-quality, site-specific data. We also use incorporate recent epidemiological evidence from Bangladesh on indirect protection from cholera vaccines. We find that a typhoid vaccination program without user fees would most likely pass a social cost-benefit test. Depending on which ages are targeted, all programs would be either "cost effective" or "very cost effective" using the standard comparisons of cost per DALY avoided with GDP per capita. Because many other health interventions have much lower cost-effectiveness ratios, however, typhoid programs are probably not a wise use of scarce public health resources. At an average total cost per immunized person of ~US$2.0, typhoid programs would absorb a large fraction of existing public sector spending on health in India. We find significant private demand for the vaccines such that the government could design a financially-sustainable program with user fees. We find that a program where adults pay a higher fee to subsidize vaccines for children (who have higher incidence) would avoid more cases and maintain revenue-neutrality. Because of higher average costs (~US$3.5) and lower incidence, cholera programs are less attractive. A program targeting both groups of children, and perhaps even programs that included adults, would probably pass a cost-benefit test. Cost-effectiveness ratios are worse than for typhoid, so the argument for allocating public subsidies to cholera vaccination is even weaker. A financially-sustainable program with user fees of ~US$3.5 is possible. Although only 16% of the population would be vaccinated, the program (with herd effects) would still avoid 329 cases over 3 years.