You can do all this in Rails without a fancy UI in a day or two
But given that they have also specified the tech stack, Iβm assuming for a person whoβs experienced in this stack would take a week full time to do something like this without fancy UI
So you can bill them 40 hours of your current rate
More realistically, they want an internal project but donβt have the bandwidth to do it themselves. So they want some sucker to do this for them.
If you are going to do this, make sure you do this as open source project so you can showcase this as part of your portfolio.