A program for cell motility assessment with a batch process function?
ImageJ has several tracking plugins, a good one being TrackMate. Most of it's functions can be scripted in various languages and the Fiji distribution can also run in headless mode. It's open source and won't cost you any mony for a much lager feture set.

I personally have used ImageJ in headless mode scripted with its own macro language because it is relatively easy to learn.
TrackMate also should output average speeds for the tracks, if I remember correctly. Otherwise you would have to write a script to measure those from the tracking data. You can use the IJ macro language, Python, Java or one of the other supported languages. 

In combination with a bash script wrapper for its headless mode I even use it in Makefiles to convert my tiff stacks to avi and put scale bars and time stamps on everything.

Hope this helps.