If $129 strikes you as a bit expensive - it seems high to me, anyway - I use this this one for $19.95 and this one for $29.88.
I bought them a couple months ago, and they both seem to perform pretty well.
EDIT: About the tether beta, with these, you're not using the camera's internal USB. You're just exporting out to an HDMI-to-USB convertor. The convertor does all the work there, so you don't need to even be concerned with the tethering software.
Once the camera is attached and sending signal, mine just pops up in my streaming software (zoom, facebook live, bluejeans, etc) as a source.
EDIT 2: For AC power, I've been using one of these 3rd party jobbers ($26.99) for over a year now and it's pretty reliable:
So I found this thing. I could theoretically plug the HDMI in to it and then would I plug the USB in to the Rasberry Pi? Not sure if the Rasberry Pi would then be able to "see" that input, but that would be awesome if it would work.