Do I Have to Pay to Use Public Domain Footage?

Dear Rich: I am working on a potential web series that would like to use material from old movie serials that are in the public domain. The first major issue I'm running into is how to properly source the film. I have found some public domain libraries that charge varying fees depending on the resolution of the movie. The issue I'm confused about is if this movie is in the public domain, what is the advantage of paying the higher fee to get it using the library? Isn't any copy of this film, even on a dvd that's for sale, still in the public domain? In most cases, the production company is doing little more than cleaning up the print for resale, and then copyrighting that process.  If video content is in the public domain, a higher resolution or cleaned-up version is unlikely to merit separate copyright protection (although protection may be granted for a colorized version). (You can review the case law in a previous entry.)
Paying for resolution, not permission. When you pay for high resolution public domain video, you're paying for access to a better quality copy, not copyright permission. Museums employ a similar strategy when they prohibit photos of public domain paintings but license high resolutions images. An additional problem with paying for these processed PD works is that sometimes you must enter into a license agreement to use them, further limiting your right to the material. (We discussed such licenses in this entry.) Generally, you're better off avoiding such licenses.
P.S. The public domain video we "grabbed" for this entry shows the mighty Perceptron - a device with an apparent gender-blending blindspot.