How much does it cost to outsource app development?

The answer in software development is always "It depends..." Who's developing the app? How well are the requirements understood? How well are they defined? Are you going with a big company or a freelancer?

It's probably going to cost more than what you initially think no matter what the answers to those questions are. If you need to go cheap look at low/no code, but understand what limitations that entails.

I would say it depends on the app being developed and for whom it's being outsourced, for example in a freelancing platform like upwork many mediocre freelancer devs ask for 100x less to build an app.

That's incorrect. If you are outsourcing to huge dev shops in the U.S. with continuous development maybe. But if you're trying to test your app and make the first version to see if it's a viable product, that's an exaggerated cost.
Here's the kicker tho, whatever the cost, it's more than what you want to pay. It's always better to find and partner with people who can build your app rather than pay, or learn and build yourself. The real cost will be stress, time, and quality as well as an understanding of your market IMHO

I'd multiply everything by 10

what do you think of doing no code development before re-building?

Based on the projects I've been part of involving app development then yes, it seems about right, but of course there are so many variables playing a role in this.

But I think you're pretty close with those estimates.