Thanks for getting back to me, nssimpson.
Since QBO is constantly changing, we can't really tell what features are still missing. With that being said, the cost will still depend on each third-party, and how many apps you'll integrate with QBO. You can contact each provider to get an estimated cost if you decide to use multiple apps.
To learn more about the recent changes in QuickBooks Online, you can refer to this article: What's new in QuickBooks Online (2018 Releases).
I'll be right here if you have any follow-up questions.
