FWIW if I were to do this I'd do

echo <input id=kmbefore><input id=kmafter onleave='alert( (kmafter.value - kmbefore.value) * priceperlitterperkm )'>

> index.html to make it available to anyone, Worldwide, for free!

For the fancy version I'd make priceperlitterperkm URL parameter to make it work not just for my area. But that's like an entire additional like of code.

My point being... I'd make a Web page, on app, no deployment, no tracking.

PS : echo "blabla" > index.html is actually becoming my new World reaching publishing method. I do have a home server with a Web server. I connect to it via ssh keys... so

ssh homeserver 'echo hi >> /var/www/self-published/index.html' and voila. I'll probably share my gist this way from the CLI.