I was just about to cancel my Giganews subscription for Astraweb and upon completing the cancellation form I was automatically offered a 2 month 50% discount - this was on the Diamond package; not sure if it applies to other packages though I don't see why not.. On the cancellation form I listed "cost" as the reason for cancelling.
Works out that I will pay $15 as opposed to $29.99 for the next 2 months - will still be able to cancel at any time regardless of this.
"Thanks for giving us another chance!
Your 50% discount will show up on your next 2 full billing cycle charges. All subsequent billing cycles will be billed at full price. If you have any questions or concerns, please contact us at firstname.lastname@example.org
Giganews Customer Support"
EDIT : This was on DIAMOND not Platinum (although might work for that too)