At $8 per month (for Prime members), Amazon Music Unlimited was already more affordable than Spotify Premium or Apple Music, but Amazon’s sweetening the pot right now with a $5 Amazon.com credit when you sign up for a free trial with promo code MUSIC5.
A similar deal was briefly available a couple of weeks ago with a $10 credit, but if you missed out on that one, this is still basically free money, considering you can spend it on anything shipped and sold by Amazon directly. You can even cancel the 30 day trial before you pay up, and you’ll still get to keep the credit. Just note that this promotion is only for new Amazon Music Unlimited subscribers.