Handling sensitive private information + pricing + legal responsability

If a client asks you for a quote to build an app that will do the following:

1. Fill out a form with all sorts of private sensitive information like:

• Social Security Numbers
• Bank account info
• Credit/Debit Card info
• passwords
• addresses, phone numbers, email, etc.

2. Save that form in a database.
3. Be able to find and modify information later.

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My biggest concern is security. Having to deal with securing SSN and passwords. Sounds like a big headache for me. But, assuming you'll go ahead and do this.

a) What would be the pricing to build this website from scratch? b) How would you deal with keeping this sensitive info very secure? c) How to remove yourself from all legal responsibility if a data breach sadly occurs?

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My language for building stuff is Javascript, so any combo of React + (any-database) + (any-API) + whatever else needed sounds good for examples.