I don't know if they are doing A/B testing or some kind of segmenting on which plans show up. Turns out it's $6.99, very reasonable for me anyway.

I used their 50 gig/6 months promotion a while back, and when it ran out I wasn't using it enough so I thought about cancelling, but the 20 gig option was what saved it for me, which in itself is interesting because the difference is only 3 bucks :-)

Here's a screenshot of dropbox.com/plans for me: http://grab.by/COT