the problem with all these cheap/easy/portable solutions is that the monitor and keyboard are at the same height. this works when you're sitting but when you're standing you really need the keyboard to be lower (at around elbow height) and the monitor at face-level. This way you're not looking down (bad for your neck) or lifting your arms the whole time.
FYI, my relatively cheap solution was to get an ikea fredrick "computer workstation" off craigslist. The item is discontinued, but they're still floating around, sometimes in the as-is section of an ikea.
many people don't bother to look up the canonical name for their desk when posting a listing so they're a little tricky to find.