The iTunes Music Store offers downloads of Ray Charles' Hit the Road, Jack 158-Song MP3 Album
. That's by far the best price we could find for such a large collection of Ray Charles songs. (For further comparison, it's even a buck under what Amazon MP3 Store charges for a 20-song compilation album.) iTunes is required to download and listen to this album.
Of note, this album does not appear to include Ray Charles' Diet Pepsi jingle from the early 1990s.