On a monthly base (total: 500-900 EUR):

Accommodation (200- 500 EUR)

Depending of the country you can be attributed a university home at reduced costs or you have to rent a room on the private market. There are colder countries and warmer: heating can add costs. 

Food (200-400 EUR)

Depending on the country, the type of food (no meat or alcohol is much cheaper ...) and your personal hunger.

Keep in mind that there is mandatory mobility within Europe:
The first year : going to the summer event can cost you easily 100-300 EUR plus visa costs
Transfer to the second country. (100-300 EUR)
The second year: transfer to the third country (100-300 EUR) and summer event. 100-300 EUR) plus visa costs.
In some cases you have to travel to research centers.

Clothing (50 EUR) 

Europe can be pretty cold in the wintertime.

In - and outbound mobility (500-1500 EUR)

Also remember that one day you have to go back and pay for your ticket as you had to the first time coming to Europe.