I just built one of these:
https://zwiftinsider.com/rockit-launcher/ I think it cost me about $40 to $50 but I didn't add it all up. I have only done two rides on it so I don't really have strong feelings either way about it yet. I am a little surprised Slowtwitch has not jumped on this train, but perhaps it appeals to more to the hobbyist crowd as opposed to the scientific/evidence based slowtwitch crowd. For me, half of the appeal was actually building the thing. I like this sort of project but to each their own. We'll see if I use it for the long term. If I like the rocking action, I will probably build something more elaborate, as again, I would enjoy designing and building something of my own.
The best part of building it was going to Home Depot where I needed help finding and cutting the lumber. I had a total of three Home Depot employees ask me what I was building. I felt pretty ridiculous trying to explain it, but the last employee I worked with that did the cuts for me had a triathlete friend and was all in on the project, haha.