Check ebay for a used volcano. I wouldn't buy anything else. There are accessories for them that make them so much fun.
Plus having bags you can make any size is a great option. You can have multiply bags for parties and huge bags for parties also. Believe me when you get large numbers of people together these options are very handy.
You can also take the volcano apart and clean it.
The vapor dome is something that people that are freaked by germs should check into. After some SEVERE alterations on ours is is now working fine. We plugged three of the four air holes, bought 1/2 inch plastic tubing that is more pliable then what came with it (the stuff that came with it was kinked and cracked also) and carefully dremeled the holes on the mouth pieces so you can draw on them without SO much work.