Your best bet is to keep an eye on eBay or Amazon over Black Friday and Cyber Monday.
I know eBay is going to have the 12 month Gold cards for 36 dollars a pop this Thursday (?) As part of their Black Friday deals. There is a thread on it in the video game deals section.
They might end up having a sale on point cards.
I mentioned Amazon because they are going to start having video game etc related Lightning Deals starting soon until X-Mas. You might catch a deal there.
I'm not sure if the Microsoft Store has a sale on them or not. If you check the Black Friday thread in the video game deals section you can find out all you need to know.
Sorry I wasn't of more specific help but good luck my fellow CAG.