I'd heard about this a while back, but just today verified it for myself - and it's true!
If you go to your local LDS Family History Center, all of which are free to use and open to the public, ask them to show you how to use their library version of Ancestry.com through their "portal". From the opening screen there will be a "sign up" offer on the right side of the screen. When you enter your email address, it will email you an offer to start a new membership for, currently, $99 for a US Deluxe (instead of $155), or $199 for a World Deluxe (instead of $299). It is only good for NEW memberships, and not for renewals or existing memberships, though. But still, definitely a GREAT DEAL!!