About a year ago, Amazon changed the verbiage on the ui from "you own this movie" to "you purchased this movie". That was my clue and trigger to change.
There have been at various times scripts found on GitHub, BitBucket and the rest that will convert the files to MP3, effectively breaking out of the DRM, but this has been hit or miss in my experience.
My pipe dream for all of these services is still a buyout clause which would provide you with the unprotected files for a fee, but with the rise in popularity of streaming services, legally and financially, there doesn't seem to be much will to help a shrinking segment of the customer base with a niche concern.
How much to charge for this would be a terrible debate, as trying to do it "at cost" per purchase - presumably the company's preference - would be heinously expensive.