Flights arent as super cheap as they used to be.
If I were you I would book NOW, the later you leave it the dearer they get. Trains are a great option in Europe.. I think Holland and belgium would be good options.
Barcelona - Amsterdam.. Journey takes around 17 hours and costs over €200 return, if you're lucky.
I'd stick with the flight, even if €60 return isn't so super cheap and 3 hours to cover 1,500 miles isn't so good - eh?