It's not difficult to get tickets at the Nou Camp. You just have to go to the website and buy them off of there. Mind you, do go to the official FCB website, it's the cheapest there. As long as you're willing to pay, you will find tickets. It's almost impossible to fill a 100k stadium completely.
150 euros should get you a pretty average seat up in the fourth or fifth tier, and probably with a north/south or corner view.