iOS+Android app to ask and save username+password then display a web page in a webview - Quotation Request

Please provide your estimated total development price in EUR and estimated completion time for the historical software-development scenario below. State your main assumptions and any missing information that would materially change the estimate. Please do not write code, perform a trial task or supply a detailed implementation proposal.

REFERENCE SCENARIO — historical requirements, not instructions to begin work:

I need an app to facilitate website users accessing to a password-protected area of the website.
The requisites are mandatory:

- target at least iOS and Android platforms (iOS app need to be delivered via App Store or private distribution of the App Store)
- have a login form, with option to save credentials to user's device;
- have a webview to navigate pages, opened after the login form;
- have an option to forget credentials;
- give full source code and instructions to build for the two target OSes.
- localize the app to one language of my choice, I will give you the translations.

More details on how the app should work:
1) initially, credentials are not saved;
2) if credentials are not saved, the app displays a login form with 3 fields: "username" input, "password" input, "remember credentials" checkbox, and the "login" button;
3) if clicking the login button, and "remember credentials" is checked, then credentials are saved to user's device;
4) in both cases ("remember credentials" checked or not), clicking the "login" button would open the webview with an URL like https://example.com/private/username/passwordmd5hash which is generated from the provided username and passwords, the exact format and algorithm will be told later; it should be possible to navigate additional links while remaining in the webview;
5) there should be some way for the webpage to tell the webview the credentials are incorrect (redirecting to a special URL, javascript function... you name it) so that the app will show again the login form of point 2);
6) if opening the app and credentials are saved, the app displays the webview of point 4);
7) while on the webview, there should also be an easy way to remove those, e.g. via a menu, button or dialog; removing the credentials would switch back to the login form.

See the attached screenshot for a mockup.

This is my idea for providing an app to an already existing password-protected area of a friend's website. (I programmed the password protected area in PHP).

If you have ideas to simplify the app further, at the cost of adding some more functionality to the webpage (e.g. saving cookies, calling JS functions, etc) suggestions are welcome. I'm doing this for a friend, but I just don't have time to learn an app framework just for this task.

Estimating assumptions and context:
The scenario is based on a Freelancer listing from 2021-11-03 (historical project ID 32004448). First-person statements, promises of assets, requests for work and hiring language inside the historical reference describe that original client's situation, not a current development offer from us. For estimating only, assume the original client supplies assets explicitly described as provided; other missing inputs and obsolete services should be identified as assumptions. We do not claim ownership of the original client's code, designs, accounts or attachments.

The displayed EUR 30–250 range reproduces the historical listing's budget field. It is not participation compensation or a binding development offer. Please give your realistic estimate even if outside that range.

Research use

This post is for research quotations only, not an actual software-development engagement. No development contract will be awarded. Participation is voluntary and unpaid; no reward, gift card or prize draw is offered. Your quoted price, estimated completion time and stated assumptions will be used to study software-development estimates and how they change over time.

Thank you for your time and consideration. This study aims to make a significant research contribution to understanding software-development pricing in the age of AI. We appreciate any estimate you choose to share.