As one of its daily deals, That Daily Deal offers the SPRI Xerdisc with Pump for $14.99 with free shipping. That's $6 under our mention from last fall and the lowest total price we've seen. (It's a current low by $18.) It's designed to improve balance while exercising and features a variable pressure to increase exercise difficulty. Deal ends March 31.
Of note, you can get two for $24.98 with free shipping.