Mix, I think Mac meant Time Capsule (right?)
Time Capsule is indeed sold, its a combination of Wifi base station and disk inside.
But you don't need one for Time Machine to work, you can use standard external drives (or indeed external RAID arrays).
And if you've already got a network in place (wifi or wired), you can just pay $20/£15 for a copy of OS X Server software that includes the server version of Time Machine so all the macs on your network can backup to a central location.