I don't have a ton of cash but I believe in the hacker culture and as an aspiring developer I figure I'd put my money where my mouth is.
It would be nice, if they'd provide an ISO. The thing I noticed about Plan9 clones and Inferno is that, they almost always run entirely in the userland. I think that's the reason HarveyOS does not provide an iso. I am not sure they are building a standalone operating system.
If you're interested you could also try inferno, however getting it up and running is also a hassle.
Lastly, in the case you're not aware, Plan9 and inferno also have a very interesting history. Inferno and Java were once direct competitors. Limbo a programming languages invented for Plan9 is also mentioned in the Dan Brown's best seller Digital Fortress.
IMHO Plan9 spirit still lives in Golang, like the Lisp Machines' spirit lives in Emacs. Maybe with cloud based OS's we could see the ideas behind Plan9 in everyday world. But other than that Plan9 remains an OS for hobbyists and idealist computer folk :).
This is a property exclusive to inferno.
https://github.com/Harvey-OS/harvey
The development seems active, the last commit was made 7 hours ago.
Last time I checked the project was still in its early stages. Docs and stability have improved a lot since then.
Sidenote: I think 9P protocol and plan9 userland like ACME editor is available on linux.