Car parking in Barcelona

[martyn94]

The last time I went in a car the costs were so horrific that I swore never again. But I will need to do so in a few weeks to drop off friends who are travelling onwards with luggage. It seems a shame not to stay a couple of days. So any suggestions for affordable parking which is accessible to downtown by public transport? It will be an old, empty, car, so the highest security is not essential.