@cwal That just means there are none for sale on eBay right now. Try a Google search for Aerobika - there are many mail order suppliers with prices from $70-90.
At Health Products for you, the price is $79.00 with 20% for first order, Save Rite Medical is $69.50. You can find others too.
I usually ask my provider for one in advance of each visit, I am billed a $20 copay, insurance covers the rest.