You don't need much spending money. All of your meals at the camp are paid for. You will need to spend your own money if you go into town and buy various items, like soft drinks, ice cream, souvenirs and things like that. You should purchase a health insurance plan for overseas travelers. Many American insurance companies (and Medicare) do not cover travel to overseas. You can get a cheap policy...
Here's the website that spells out the Poland program in detail: https://globalvolunteers.org/poland/