Nobody dreams of paying for formatting software. And yet here we are, because the alternative is you versus a LaTeX template at midnight, and midnight you is not your best self.
The free tier of an academic paper formatter app does a lot. Template application, basic reference checks, page limit warnings. For most papers, most of the time, free is genuinely enough. I say this as someone who has paid for things he didn't need: start free, and upgrade only when free hurts.
When does free hurt? Three situations. One, you submit to the same venue family every year and want its exact template one click away. Two, you're formatting for coauthors who can't be trusted with templates. And by can't be trusted I mean all coauthors, including you. Three, you need a paper formatting checker SaaS with real verification, the kind that validates margins and fonts against the venue spec instead of eyeballing it. That last one is where paid earns its money.
What's never worth paying for: formatting advice. If the tool lectures you about good writing while misformatting your references, walk away. Tools should do checks, not give opinions. Opinions are what reviewers are for. You've got plenty of those already.
My honest stack: a free academic paper formatter app for drafting, a paper formatting checker SaaS pass before submission, and for the submission that really matters, an actual paper formatting service with a human who's seen your target venue's template a hundred times. The last one sounds extravagant until you price your own time. Then it sounds cheap.
confjournal.fyi offers paper formatting and submission checks for your target venue, the human-checked kind, for the papers where it counts.