Use Firebase Cloud Messaging (FCM), previous version known as Google Cloud Messaging (GCM), is completely free of charge. See Firebase Pricing:
Included Free
Analytics, App Indexing, Authentication, Cloud Messaging, Crash Reporting, Dynamic Links, Invites, Notifications & Remote Config
A quick Google search shows that there is an available FCM Cordova Plugin. Then you should go ahead and make use of Topic Messaging. From the plugin link:
Subscribe to topic
//FCMPlugin.subscribeToTopic( topic, successCallback(msg), errorCallback(err) );
//All devices are subscribed automatically to 'all' and 'ios' or 'android' topic respectively.
//Must match the following regular expression: "[a-zA-Z0-9-_.~%]{1,900}".
FCMPlugin.subscribeToTopic('topicExample');
The idea is quite simple. Simply have all your users subscribed to a topic, then send a message towards that topic, and it should be delivered to all of them.