I can't recommend EVS enough, I feel so blessed that I have been given this opportunity!
I work in a social centre with people with mental health problems in a stable condition. I work 3 hours, 5 days a week, running groups like yoga, art, running, cineclub and music. Every Friday we go to see a new exhibition around the city and I also teach two classes of English. The people are incredibly supportive and the foundation are even paying for me to do a language course 4 mornings a week at the university.
It was hard at first, because I've never studied Spanish. I arrived and couldn't understand a word anyone said. They expected this and helped me slowly build up to running groups. Its a great way to learn a language because you are fully immersed with Spanish people. Its even easier in care work, because the users are always keen to talk to you. My top tip would be to try to make only Spanish friends even if you can only talk together in English at first. There are lot a of locals keen to practice their English. You end up talking more and more in Spanish. I spent 8 hours with a friend last Saturday talking only in Spanish, with some hilarious results! Its also the best way to learn about the local culture &often gives you some great links for visiting other cities.
The money varies from project to project. The EU cover basic costs like accomodations, utility bills and a food allowance, but some projects provide a little more money from other sources. How much you need to save depends alot on how you live. For example, I receive £315 spending allowance every month & my housemate lives with in tis budget. I spend £100 of my own savings, so I can go out for tapas a lot with friends but don't splurge unnecessarily.