For 8' high, strength, and cost, you cannot
beat renting scaffolding and then building 2x6 framed platforming to go on top.
You will need to visit your local scaffolding rental place or look up scaff rental/sales websites and make sure you are totally familiar with the standard shapes and sizes. They are not inherently 4x8 friendly but with careful planning you can achieve what you need. You will have to frame above the
level of the corner "posts" and take into account x-bracing limiting some access underneath. "Walk-thru" type scaffolding is your friend. Do not forget
leg levelers and coupling pins. As noted, it can be noisy but this too can be overcome. Also be sure to work out with the rental person that you want clean stuff or you might get a load of scaffolding loaded with caked on concrete which is awful to work with. They are used to renting by the week or month and most will deliver and
pick up (for a charge).
I once did a production of "Good Woman of Setzuan" with mobile platforms of castered scaffolding. I wanted it in bright red as the platforms would be totally exposed. After a few phone calls, I found a rental yard that had exactly what I needed. I mentioned it was for a
theatre production, and without missing a
beat, the clerk said "Oh, we do that all the time."