There are many ways to get finacial support. At first it depends on the organization and the program you choose.
In the most cases you get financial support from your government to
cover the flight expenses.

Interns are provided wages by the host.
The wages are high enough to cover your life expenses and social activitys.
In addition you should have savings if you want to by a car or for trips in the country.

There are also mostly chances to earn extra money in your field ( it has to be confirm with your kind of visa).