itunes

Just because you subscribe to Apple Music does not mean that you lose the ability to purchase music. Note that an Apple Music subscription gives you rights to listen to music only as long as you continue to subscribe while you retain rights to purchased music indefinitely.

To download Apple Music without purchasing, see: Add and download music and video content from the Apple Music catalog - Apple Support

Because having an Apple Music subscription does not in any way preclude the possibility to actually purchase songs.

The iTunes Store will always charge you for songs, as it is a store.

If you want to download songs through the subscription service, use the "Browse" and "For You" sections. No prices will appear there, and you can freely download from there as long as you are subscribed.

Do note, as mentioned by FoxFifth, that anything downloaded from the Subscription Service (Browse and For You sections), will only be available and playable while you have an active subscription. Cancel the subscription and all music obtained through it will stop playing and eventually be removed from the device.

The iTunes Store is there so you can actually buy the item, and keep it even if you cancel the Apple music subscription.