Forms Customer Validation

Forms Customer Validation

Hello,

I would like to create a public-facing form for someone to register for an event.  We are not using the Zoho Backstage App.

I would like the end user to fill out the form.
  1. There is a field where they can put in their customer number.
  2. If that customer number matches a customer record in the CRM they are charged price A.
  3. If that customer number doesn't match they are charged price B.
SInce this is a public-facing form I am not sure how to accomplish this.

Any ideas?  I am ok if we have to do some custom dev to accomplish this I just don't know where to start.