Perhaps this post can put you on the right track:
You will need to become familiar with some of the following:
• Math column: Allows you to make calculations based off basic number columns.
• User-specific columns: Your basic columns are either global (all user of the app see the same data) or user-specific (two users will see different values of the same cell). These are used in calculators if you want each user to have their own calculations within the same calculator.
• Choice component: Might be useful if you have multiple services to choose from in your calculator
• How to create a custom form by @Darren_Murphy. A calculator is a use case of a custom form.