We are planning a 5 day trip to Barcelona and due to a limited budget we were thinking of staying in Gavà and then travelling to Barcelona, practically every morning. Do you consider this as feasible ? Is Gavà included in the Barcelona Card ? Or do you recommend a better solution ?
Well it's only twenty kilometres from Barcelona, so from that point of view, yeah it's feasible. I've done a similar thing in the past for Valencia; staying just outside of the city. It'll take you about 25-30 minutes to drive to the center of Barcelona from Gavà.
Gavà is also very close to the airport, which may be handy depending on how you are arriving.
But consider - if you weren't planning on hiring a car (or don't have one), then you're adding the cost of a car rental, insurance and petrol to your accommodation (as well as using an hour of your time each day) to stay out of the city you were trying to visit. This also restricts your night time activities if you're planning on drinking.
I'd be surprised if you couldn't find somewhere in Barcelona to stay which works out the same price as commuting from Gavà.
If you're not using a car, and want to use a bus to get into Barcelona, ten bus routes link Gavà to Barcelona, surrounding towns and the most important neighbouring places. For more information contact the Autobusos MOHN bus company, or check the timetables on their website. It would appear they run every 45-60 minutes, depending on the day of the week, although evidently my Castellano is not good enough to find how long it takes.