hi katarina, you have come to the right place.
as an ex-spanish teacher in u.s.a., i'm sure your teach would not want us to just GIVE you the answers

but rather show you where to find them and do the research on your own
- if ya give a man a fish, he eats today, if ya teach him how to fish, he eats forever (or something like that) -
there is a website at
www.segundamano.es which you can use to look up the costs for a studio apartment, flat, house and a summer house just about anywhere in spain.
just go there and enter the "Inmobiliaria" section.
the rest we will leave up to you.
if you run into a snag, let us know and we can give you more tips.
if you find that the spanish is overwhelming, i can direct you to another site for this research but that has an english version but i think you will learn more if you use the
www.segundamano.es site, even if you have to struggle through the spanish.
saludos,
jer... once a teacher always a teacher