The cost for registration is $3n+3, where n is the number of main events you're registering for, with a $21 maximum fee. This means that each event after six events is free!
$1 of the registration cost will go to the World Cube Association.
Because Skewb is an unofficial event, the cost for registering for the Skewb event is $0.
Skewb is an official WCA event as of January 1, 2014. To commemorate this momentous occasion, the cost for registering for Skewb is STILL $0! Yay! ~Ranzha