In the "What's new with Alexa?" newsletter this week, Amazon has the following offer for current
Amazon Music Unlimited subscribers:
For a limited time, current paid Amazon Music Unlimited subscribers can get 2 free months of Family Plan, with music for up to six accounts, when they upgrade their subscription. $14.99/month after.
And, it actually applies a $30 credit, so if you go with the annual plan, it will be discounted to $119.00, making the family plan under $10 per month after discount.
Link for offer page:
On the offer page, it says to enter coupon code TRYFAMILY
If the link doesn't work (it doesn't work for me anymore as I already redeemed the offer), then go to the Amazon Music settings page and click "Have a promotional code?" and enter the "TRYFAMILY" code.
Here's a link to the settings page: