A few years back we decided to do a ball pit idea - we wanted to have the pit around waist height....unfortunately to fill a 12X12 room that deep with standard ball pit balls would have cost us a fortune. We ended up going with 10" beach balls. Under the beach balls we had 2 air cannons set up....when the guest got to the middle of the room the air cannons went off sending the beach balls everywhere.
Was a cool effect....the down side was the beachballs were very hard to move through, instead of gliding over each other they kinda stuck....and then as people pushed through they would all pile up at one end.
I would love to revisit the idea - is there a wholesale place to get the ball pit balls in bulk????