Google Music offers downloads of a selection of Greatest Hits and Best Of MP3 albums for $3.99 each, as listed below. (Amazon charges the same for many of them.) That's the lowest price we could find for these DRM-free albums. Some notables:

• Jay-Z's The Hits Collection Volume One Deluxe Edition (pictured) for $3.99
• Frank Sinatra's The 20 Greatest Hits for $3.99
• Guns N' Roses' Greatest Hits for $3.99
• Billy Joel's The HIts for $3.99
• blink-182's Greatest Hits for $3.99
• browse more Greatest Hits and Best Of Albums at Google Music

Of note, you'll need Gmail and Google Wallet accounts to access these downloads.