Those of us who don't live in Brazil (or are on an organized tour) will have to wait until early 2016 before the worldwide lottery is held. Day session prices range from $42-147,
evening sessions are $109-378 and something called a Super Final (I can only guess that this is for the 100 meters, but might include more dates) are priced at $147-504.

Here's a link to the info and this link also contains a further link to specific ticket prices for all events: