The price book is a static file the page fetches so it can do the arithmetic. Your scenario is not sent with that request.
Fonts load from Google Fonts. That is a request to Google for the typefaces, separate from anything you type.
On looptally.io and this project’s vercel.app host, the page loads Vercel Web Analytics from /_vercel/insights/script.js. That script records a page view on Dan Mercede’s Vercel account: the address of the page and a visitor count he can open. It does not receive the numbers you type or any text you paste. A local preview does not load it.
The workbook checkout, when it opens, is the payment provider’s page. Their privacy notice applies to that purchase. Looptally does not receive your card number.