Yes Conversations is still a paid app on Play Store. The F-Droid version also doesn’t support Google cloud notifications so some message notifications will go missing occasionally. For Android there’s also Quickly which is a Conversations fork and aTalk which works OK but reminds me of 90s Windows software. It’s still quite usable though. Honestly Conversations is totally worth the money if only for the amount of effort gone into modernising the platform which also a testament to its extensibility.
I run a small server for my family on a cheap VPS. We’ve been using it for about 5 years now and it’s chugging along. It’s simpler and lighter than Matrix (at least from the server’s point of view) but the user facing side could use some polish. It’s perfectly fine for one to one chat. I wish it was more popular for group chatting.
Here’s a list of good servers if you want to try it out. You will also need a client. Check one with E2E suppo ort (called OMEMO in XMPP).