Our exercise ball was about $10 from Target. It's pretty large, taller than Tara for sure. I saw some smaller balls today, about half the diameter of my exercise ball but still bigger than a dog's mouth, for only $2.88- think the kind you see in grocery stores in the big wire cages.

Tara NW1 ORT-AC CGC - GSD 2008
Suli - DSH 2006