beans, $700 / metric ton [1]
rice, $500 / metric ton [2]
a meal of 65g dry rice and 55g dry beans per person.
700m * 3 = 2.1b meals per day 115,500 tons beans = $80.9m 136,500 tons rice = $68.3m
Total $149.1m/day
I'm sure at these quantities you can get much better prices of rice and beans, even just browsing on alibaba. I'd guess we can probably get that down under $100m from alibaba. Probably even lower at the quantities we're talking about.
1 - https://www.alibaba.com/product-detail/red-bean-wholesales-s...
2 - https://www.alibaba.com/product-detail/Jasmine-Rice-Long-Gra...