They said they were using it for side projects. Even if Google is subsidizing the bill, I'm interested to know how much something like this would cost.

Google does not provide any discounts for employees personal projects.

Cloud Shell is free up to 5GB additional storage is $0.02/GB a month.

Alternatively someone linked https://www.gitpod.io/ which also has a free tier.

I don't know about Google, but as far as I heard, AWS folks pay for their own AWS resources for side projects, at least.

Google too.

Microsoft does give cloud credits per month for employees tho.