For your use case I think e-mail is the best option. One scrappy alternative I've used with success in the past is to use a messaging app like Telegram. I neede

For your use case I think e-mail is the best option. One scrappy alternative I've used with success in the past is to use a messaging app like Telegram. I needed push notifications for a small website but all the "Push apps" (like Pushover) that I found were quite expensive. Telegram is free with a simple but powerful API. However, this is only viable if your users are either from a country that already uses said app a lot, or like your site enough that they are willing to download an extra app for it. I wouldn't recommend it as a required thing but only a bonus. Now that browsers support push I've been using that, but for iOS it's still a bit painful and doesn't play well with my site that uses many subdomains.