I decided to open an Microsoft Azure account, and use the $200 in free points for new members to render a better version of my colony ship panoramic scene [edit: click here for an external view]. I was still unable to add atmospheric media and radiosity inside the station habitat. They simply take too long to render, even with dual 8-core CPUs and 32GiB of RAM. If I could afford several virtual machines linked together to form a render farm, maybe it would be feasible to enable them. But that would cost a lot more than the points I have available, I think.
Google Cloud has a similar offer for new customers, but limit you to a single CPU with 4 cores and 8 threads until you “upgrade” your subscription. So I did not find it very useful.