Developing an app from scratch can cost from US$1,000 for say a simple game through to US$10,000 or so for something useful, and upwards for more complex apps requiring code innovation.
Major apps usually support an entire business and the cost may not even be quantified: Facebook, for example, is an app. Developed of a decade, it has probably had tens of millions spent on it, but this seems hardly worth counting compared with the company's US$200 billion market cap. See The app as a business for more about building a business around an app.
The basic cost of a H-DAM app is from $5,000 for a single platform (eg iPhone/pad). This is for a standard format app and excludes any customisation and initial data entry.
We give non-binding cost estimates at no charge, based on your description.
We give binding quotes based on preparation of an agreed functional specification. Any changes from the specification may of course incur extra costs. The functional specification is charged for and is yours to keep; if you go ahead, its cost is deducted from your quote.