Copied from Slickdeals.net forums:
INSTRUCTIONS TO LOCK IN $79 RATE
Quote from orick:
If your current Prime membership is scheduled to expire on or after April 17th, and therefore would auto-renew at the $99 price, you can effectively lock in the $79 price by taking the following steps:
(1) Look up your Prime expiration date. (Let's say yours is June 11th.)
(2) Purchase a Prime Gift Membership here: https://www.amazon.com/gp/prim...
Set the delivery date as the date after your membership expires (in this case, June 12, 2014).
Enter your own e-mail address as the gift recipient. It is okay if this is the exact e-mail address already associated with your Amazon Prime account.
Place order (total will be $79).
(3) Turn off your Prime auto-renew. (End membership - at expiration)
(4) On the day after your membership expires, you will receive an e-mail from Amazon with the gift membership. Follow the instructions to apply it to your account.
This is a pretty straightforward way to save $20.
HOW TO CANCEL AMAZON PRIME AUTO RENEW:
Go to Manage Prime Membership https://www.amazon.com/gp/subs...
Review the renewal date listed on the left-hand side of the page.
If you currently have an Amazon Prime free trial, click Do Not Continue .
If you currently have a paid Amazon Prime membership, click End Membership .
Turn off your renewal using the link below the renewal date.
Note: Your membership will expire at the end of the current period. It will NOT end before your current paid subscription is over, nor can you cancel it early for a refund.