The umbrella Association for all the Escolas de Samba from Rio, LIESA, has just published on its website the prices of tickets for carnival parades at the Sambadrome in 2008 : Ingressos Sambódromo 2008. For most tourists the interesting part are the Arquibancadas, the stands. On the same page there is a map of the Sambadrome (click on the link on the top right hand-side corner of the page).
The escolas de samba enter the sambadrome through the bottom side of the map (the bit labeled Área de Armação, and known as Concentração). Tickets for Setor 1 are cheap because you don’t get to see the schools parading – only their preparations.
The parade finishes on the top side of the map, on the part known as Praça da Apoteose (not labeled as such on the map). Tickets for this part of the sambadrome are also cheaper as you only get to see the end of the parade, when the escolas are already tired after a performance of more than one hour.