I stumbled across this great exercise tool during rummaging in sport goods (on of my favorite activities 
) and directly bought it. I train and work (during personal training sessions) versatilely with physioballs and missed an extension untill now with whcih allows you to widen the repertoire of exercises. Here it is, for 19,90 .- SF (around 20 $). Great thing, and quickly pumped up. The purchased parts package contains a small pump (which is sufficient for the air ring, compared to pumping up the balls with such a small pump would make you sweat), 1 substitute valve and 2 fitting tubes. Available in all Migros SportXX stores.
Ball Air Ring 1
Ball Air Ring 2