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I use a $15 Target TV tray. I took the legs off and it makes the perfect lap desk.
Edit: couldn't find the one at target but it's basically this but black and I use a giant mouse pad.
Not exactly to your specs, but I’m sure if you look on amazon for a few you can find something to work.
This isn't exactly the same, but it gives an idea of how these fold...
I've used this table to stack two combo amps: [link]
I'm not sure what you need other than a work surface, but the first thing that came to mind was a portable table like those from Lifetime. That's what I have used in the past to reload ammunition in the living room. Similarly, the older style tables made with particle board are heavier and a bit more stable. You could probably find one of the old style tables on craigslist or in a local store since they are so heavy and expensive to ship.
Also, if you need greater stability, contractors and handymen use portable work benches like this. I use a workmate for a miter saw stand all the time...so it is quite strong and stable. You could use it as a base if you want to make and add a top to it.