After I saw the post from the person who got a 636U for $49.97, I checked the website, and the 636U was listed at $49.97, too.
I went out to a few CompUSAs, and to make a long story short, the dozens I had seen a few days ago were all gone, and I bought a rain check.
On the way home, I looked very closely at the ad, and saw that there were TWO product codes on the bottom of the ad: #264027/#279750. The first one is for the 610U, the second is for the 636U.
In all my travels, I have not seen a single 610U.
So you can get a 636U for $50.