Tangential: I've had good luck over the years with this flow:
-Buy on Amazon (using a single card!)
- Install an old version of Kindle for PC (might be able to find an installer online); download/open the book in it
- install a Calibre de-drm plugin.
- Open the Kindle file downloaded to a home subdirectory in Calibre.
- Convert to epub in Calibre, using one of the big HD formats etc so it won't downscale images
- save the epub somewhere you can back up, and also transfer it to your reader.
Yikes ... I guess I wouldn't recommend this as an easy solution!