If you prefer to own equipment rather than rent, there are few options in the city where you can purchase film equipment.
In the Sant Antoni area there are numerous stores that sell photo related equipment, including 2nd hand, which is a good place to orient yourself if you prefer filming with DSLR photo cameras or consumer level video cameras. The area also hosts many stores that will sell computer hardware, such as hard drives. One famous store focused on sales for more professional video and audio equipment called Nivell10 closed in 2014. The rental house MasQueVideo also in Sant Antoni also does sales for prosumer and professional video equipment through their website.
The La Verneda area on the north/east corner of Barcelona is home to some very low priced Chinese import photo equipment warehouse stores reference/details needed. Cheap lighting equipment bought here offers a low cost alternative compared to expensive studio to the indie film maker.
For buying online, the New York based megastore B&H Photo is a popular outlet for film makers worldwide due to their enormous variety in inventory. However, please take note that items purchased online will require payment of import charges.
Sources for second hand and low cost imported equipment are Segundmano.com and eBay.