You can get street view images from maps.google.com for free, so a scraper should be able to use the same interface for free (as long as it's either not throttled, or you can get multiple IPs or don't care about speed).
As you say though, another way to go about this would be to scrape the public SV site, which I have not attempted to do. @xnx linked this project in another comment, which seems to do just that: https://tllabs.io/google-street-view-hyperlapse-youtube-vide...
I don't know if/how they evade captchas.
Going back to your first comment, I originally made this as part of an app with an interactive streetview component. I reused the initialization code I had as the base for this. Re-using that code also makes sure the screenshots taken would be close as what you'd see using the embedded streetview (In our project we had a bunch of remote locations without a lot of SV images, so depending on the search radius used when querying for a panorama, we could end up in vastly different places).
However, I realize that I never even considered scraping the public site, which would allow for hiding your identity by not needing an API key. I'll think about this.