There seems to be a misunderstanding here, backups in cloud storage are a fraction of the cost of data in Firebase. I used to work with a 300GB Firebase instance and we never worried about backup costs.
I clicked the link to the script at the bottom of the blog post thinking it would be a github link. It downloaded a file with the contents "Please provide your databaseURL." Seems like the script is being executed by the author's web server instead of returning the contents of the file. It was also a (hopefully) friendly reminder to myself to not click random links on the internet without checking where they go.
I think the author has a fundamental misunderstanding of how the built in backups work. The backup likely goes into Google Cloud Storage which is relatively cheap.
Aren't you spending a lot of money downloading the database through Realtime Database though? How does that compare to the cost of the built in backup?