The most convenient and fastest option is an airplane. The cost of air travel is 80 - 120 EUR, the journey time is 1 hour 10 minutes.

For those who are not looking for easy ways: There is an option to get from Barcelona to Lisbon by bus, the ticket price is about 70-80 EUR. But this option can not be called fast: the journey time is 19 hours.

The journey by train will take about 16 hours, while you will have to get to Madrid from the beginning and already there to catch a train to Lisbon. The cost of the ticket can be found on the website of one of the Spanish railway carriers: www.renfe.com