Just in case anyone might be thinking of making a Van de Graaff generator soon, this is an ideal season to find a cheap dome. Maybe.... Now that the holidays are almost done, many stores that have been stocking "ornaments" filled with candy or cookies will be discounting them. (I have a hunch most of these spheres are gonna be steel instead of aluminum, but you might get lucky. Or, steel might work out okay, I dunno.) They also generally seem to have a few holes punched in them, maybe so they don't get vacuum sealed when someone tries to open them.
Drugstores and Target often have these hollow metal ornaments filled with candy. If you want a small generator with a flattened sphere, try one of the M&M containers. A couple years ago, Pier One had some cookie filled ornaments. I was just at a Staples, and by the register they had a ~7 inch sphere filled with chocolate cookies for under 3 bucks. That one is definitely steel, and the metal does have some minor ripples cuz it's just a container, not something that should be nicer. Plus, there's a plastic piece that holds both halves together, so you'd probably have to use some solder to hold them together and let the electrons flow freely.