Amazon’s “SD” option is roughly 480p. If you purchase the episode on Amazon Video and select SD download, you are legally obtaining a ~480p file.
Searching for "ghosts s04e01 480p" on public trackers reveals dozens of results within hours of the episode’s airing. Common release groups (like , x265-club , and aAF ) often drop 480p x264 rips. ghosts s04e01 480p