looking for accommodation in madrid

i am a student and i am going in spain for studies in urlc.i am from greece . i am coming with the erasmus program . i would like to find a flat very financial and modern near to the metro station and to super markets. i look forward in order to find the best option of my apartment! i will come in september and i will leave in december . i would like also to host my freinds some days , so if i will live with roomates , i would like to have my personal bedroom . i would like a cheap solution because i am a student and i wont pressure a lot my parents .