How much money do I save if I pay Apple Music yearly instead of monthly?

Apple doesn't advertise yearly plan prices anymore. You can look in Setting for your monthly plan and there should be a option to "See All Plans", and if the yearly subscription is possible, it will show the price for that there.

How to switch to a different subscription plan - Apple Support

I used to pay yearly for Apple Music, but when I switched to Apple One, I only have the option for the monthly plan.