The other day I was coding an interesting project via Upwork for a guy in US. The point of calculator was to provide the visitor information about what would be the most cost efficient way to eat when visiting Disney World. I have personally not been to Disney World before, but looks like you can choose between predefined dining plans or buying each meal separately.
There are number of restaurants withing the park (close to 180) in different areas. Restaurants provide different service methods (quick service, table service or just a snack) and have different pricing, some are cheap, other expensive. Visitor can further choose between several extra options for drinks and deserts.
The user stays on the same page from the beginning to the end due to Ajax usage. This way calculator can be easy integrated into any web page as iFrame or in any other way when running on WordPress and other frameworks.
You can find a live version of calculator here: https://disneyworld.rešitve.si/
Play around and see how it works.