Easy: don't. Seriously. Take the Seabus across then hop on the train to Stadium and then you have a 2 minute walk.
Parking for a major concert is $15-20.
Grims is right, take sky train. IMPARK raise their prices according to events. I wouldn't be surprised to see parking OVER $30.00. Those scumballs manipulate pricing depending on event(s) and if there is more than one event going on at one time they really "Hose" the consumer.