I have lived in Barcelona in the past and still spend considerable time there every year. If you are a Spanish resident (independent of your citizenship, but you have a Spanish and/or EU resident card) with a legally declared and registered address in Barcelona, in other words, 'empadronado' en Barcelona, you can easily rent at local prices, especially if you have verifiable income via monthly bank deposits and/or job contract in Spain or in the EU.
If you do not fall into any of the above categories (you are not a resident, you are not empadronado in Barcelona, and are neither Spanish nor EU citizen), the conditions are similar to what you may find in BsAs (sublets and rent-by-owner). regarding this route, my impression is that there are more sublets and flat shares available at any given time in BCN as compared to BsAs (may be my impression only) and that, based on my experience only, especially if you speak Spanish/Catalan, the owners are very much willing to work with you regarding security deposits and other details. Keep in mind that renting a studio in Barcelona for under 600-650 euros/month is not easy, however, it is also true that once you start adding bedrooms (i.e. 1,2,3) the price does not go up that much.
Lastly, if you are a native resident of Catalonia (i.e. Catalan by birth or family) you are eligible for special rates on rent and purchase of property, hence having a Catalan partner (even de facto) will work in your favor.
