Hi Bethsu,
You are right they will ask you in most of the cases to have a bank auction, it use to be the price for 2 months renting. But I am not glad to tell you that you will have serius problems to find a place to rent as this is in my opinion the bigest problem that young spanish people have. Check prices in this URL
http://www.idealista.com (if you need help using the web tell me) and you’ll start to know what I am talking about. Maybe if you have a medium US salary won’t have problems but if your salary will be acording to what it is paid to a standar Spanish I can only tell you that you won’t be abla to rent by your own and you should start thinkis to share a small flat (I’m talking about preces in main province capitals overcome at Madrid)