The Ninja Master Prep is typical of most products sold through infomercials - in that TV is the primary way they advertise and generate sales. Like any "As Seen On TV" product however, there are locations where you can but it.
NinjaOffer.com - Link
This is the main company site, which sells the Master Prep for $59.85. with free shipping.
QVC.com - Link
It`s a little more expensive here at $58.46 with Shipping & Handling of $7.72.
Bed Bath & Beyond - Link
Retails for $49.99 each with varying shipping costs.
Sams Club apparently has them for $49.95 and comes with one pitcher and three processor cups. I have not confirmed this myself.
Wal-Mart has been reported to have them at the $49.99 price point as well.
eBay has tends to several, both new and used.