You should reach out to Joe (@Finsweet) here on the forum, he’s fairly active and I’m sure he’d have no problem answering any questions you have about the site.
It’s not super complicated to do with js, granted their implementation looks a bit different than I would have expected. Essentially they have form elements that on click are checking for other selected elements and creating a total and then adjusting the pricing and text in the calculator accordingly. As @mikeyevin said I’m sure Joe can provide more detail.
I don’t think you can do this without a developer though.
Yes, there is a lot of custom code on our site! We built the pricing section in Webflow Interactions and then rebuilt is using Anime js library for performance. Most of what you see on our site can be built with Interactions!
As for the pricing calc - yes, this is built with javascript. It’s also hooked up to Webflow CMS! It even passes values to the contact form! Really custom all around. You’ll need a js dev to help with a calculator like this - but it’s not difficult for most js devs.