You don't need an expensive AF system to pull focus for video these days.
The Focus Maker from B&H Photo is a great alternative at $40.
This easy to use focusing device worked beautifully on both my 77m and 58mm lens (fits any lens size). Only used for 2 shoots, so its in mint condition with not one part missing.
Bought for $90 USD, it was only used for a handful of shoots so its as new.
Comes with everything you see in the photo.
*Check out the Vimeo link for a better understanding of how this gadget works