The Escuela Oficial de Idiomas is definitely the cheapest place to learn a language in Spain. Therefore, lots of people want to get in. Every year there is a toss to choose a letter. People whose surname begins with that letter get in first and the rest follow them in alphabetical order.
Spanish for foreigner at the Escuela is slightly different that the rest of the languages. They have semi-intensive courses that last for about 4.5 months instead of 9 months that we have to study in the rest of the languages.
Note also that the website provided by liuxiahui
is only for the Escuela Oficial de Idiomas at Jesús Maestro (the central one) but there are others around Madrid and Spain. Check out
Escuelas Oficiales de Idiomas