Some questions are almost always asked when creating an app. As is often the case, there are no universally true answers, but here you'll find mine.
Why so expensive?
Software is very complex, even if that's usually not visible by the end user. An app is comparable to a car. The rapid development of today's software is only possible because there's a lot of prefabricated components.
Extensive knowledge is required: What components exist and how do they interact? Which parts have to developed from scratch and how can security, realiability and performance be ensured? Software development is no mass production and demands not only a vast know-how but also a lot of commitment.
There's certainly a cheaper way...
Of course. The quality can be reduced; "invisible" features like security can be omitted. Also, different developers have different prices. However, there's usually a direct correlation between costs and quality.
Work with a developer that has the same values as you.
Good preparation and planning saves a lot of effort. Identify your exact needs and requirements!
How accurate is the cost calculator?
The cost calculator should only be used for an initial estimate.
Every project needs to be assessed individually.
Is it possible to develop only once but support multiple platforms?
Usually not. While there are several solutions that promise exactly that, the operating systems and interface guidelines are usually just too different. The effort required for the (generally small but numerous) adjustments outweighs the time saved in the first place.
Are HTML-based apps (with native wrapper) worthwile?
No, you just end up combining the disadvantages of both systems. Bad performance and poor usability are usually the result.
Programmers favor the technologies they already know - and that's alright. But it's important not to make decisions based on this.
If performance or hardware access (GPS, camera etc.) is required, then a native app is the best solution.
If the app only needs to present some information, a website optimized for mobile devices is a good alternative. While it won't be available in the app store, it is much easier to update and manage.
My web/print agency has created a design
Ascertain the feasability with an app developer. Designing for print or web is very different from conceiving a mobile app GUI.
This is all too complicated.
Find someone that can advise you. In the region of Zürich (Switzerland), I might be able to support you. If you're interested, just contact me.
I have a question not answered here...
Write me. I will try my best to help you.