A custom web app cost is the fee to build the first version someone can log into and finish. It is not the fee for every screen on a whiteboard. Small businesses overpay when the quote is for the imagined product, and they underpay when the quote is for a brochure that pretends to be software.
What the first release should be
One user, one job. A customer portal that shows their orders. A booking tool the front desk will actually open. An internal list a field team updates. Accounts, the happy path, and the failure states: wrong password, empty list, a save that did not work. The next role, the mobile app, and the reporting suite are later milestones.
If a fast website would do the job, we will say so. Mobile and web apps is the service, and the website-or-app note is the longer version of that choice.
How it is billed
The amount is written against that first release. You pay when it matches the scope. There is no advance, and the code is yours. Hosting after launch is a separate, smaller decision.
Questions
Is a web app the same price as a website?
No. A website explains an offer. A web app has accounts, data, and a job someone finishes every week. The first release is priced as that job, not as a page count.
Should we build the mobile app first?
Usually no. If people will not install anything, start with the web app. A phone app is justified when they return daily or need the camera, notifications, or offline use.
Who owns the code?
You do. The repository is part of the handover. You pay the milestone when that release matches the scope.