Today is the final day you can lock the old Premium rates. On December 1st, Premium rates will be changed to: 

$3.99 - 1 Week ($0.57/day)
$9.99 - 1 Month ($0.33/day)
$39.99 - 6 Months ($0.22/day)
$49.99 - 12 Months ($0.14/day)

If you want to find out how you can keep the old rates indefinitely, refer to Pete Hoefling's announcement article with FAQ here:

http://www.starcitygames.com/magic/misc/25169-StarCityGamescom-Premium-Announcement.html