I went to a barcelona real madrid game last year at Nou Camp and used www.sportsemotions.com. Ticket prices were reasonable, however search around on the internet and phone up and ask for discounts. I was in spain working at the time and looked for another way but basically its very difficult to get these tickets on your own, especially for such a big match. These clubs normally sell their tickets at half price to signed up members of their football supporters clubs so since these agency's are usually members of the supporters clubs the mark up on the tickets is not huge over the face value of the tickets. A lot of the tickets they use are also season ticket holders tickets who are not going to the match. I paid under 100 euro for the ticket but it'll cost you at least 80euro. Going on the fact that easyjet and ryanair both fly into barcelona, the multitude of hotels available there at reasonable prices and the ease with which you can get to the stadium by public transport you would be better off organising transport and accomodation yourself.