Please don't feel obliged to pay anything. Consider this a free download with an optional donation.
If you choose "free" I am asking for your e-mail address, which I'm only going to use to let you know when I release new music (which is often free) or go on tour. No spamming or giving your address to others I promise! And of course you can unsubscribe any time. But I don't want to force anybody, so if you'd like to download the song for free with no e-mail address, just visit http://www.last.fm/music/Digits/_/Nonstop and you can get it there.