Cheap Airlines flying to Barcelona do charge more to get there than to other places, but it is a very popular destination for a reason: it is beautiful!
Anyway... once you arrived at the airport, you will quickly discover that the easiest connection to the centre is by bus. It costs 4 Euro and gets you right into the centre. Don't get off at the wrong station though... Placa de Catalunya is not the same as Placa de Espana! (or however these places were spelled)
Our accomodation (Hi Hostel Las Ramblas) was smackdab in the middle of downtown Barcelona - perfect! They have mixed dorms with comfortable beds, unfortunately there werent enough showers which led to long lines in the morning and the free breakfast is ok, but it is no loss when you skip it. People are friendly and staff is generally helpful. So, I can recommend going there!