This is a great conversation to see. I also was a bit surprised by the large jump in Meetup.com subscriptions for not much in return.
I know there's quite a few of organizers that are switching over to using
Luma for setting up events and collecting RSVPs. It's free and pretty easy to set up. I also had conversations with their support team and it was a very quick response time and easy to navigate system. You can basically do all you need to do on the Free part of the service. If you are a non-profit, they do also have a 40% discount to their paid service.
Discord is another free-to-use application and has been growing in popularity (at least I believe so). This has functions to set up events and RSVPs and you can also have live chats/video streaming, etc.
I hope this helps...
Cheers,
Ally