Costs vary per country and trip. Trip costs cover all transportation, lodging, meals, excursions, and outreach experiences. The only outstanding cost would be a Visa application fee depending on the country and some spending money if you wish to bring back any trinkets!
The fee is $100 application fee for new volunteers +cost fee + flight for each trip. Specific costs can be found on each opportunity at https://oneworldhealth.servicereef.com.