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.