Not sure why two-pieces are needed or why one needs to float. Or if a $68 rotor stops better than a $15 one.
Floating rotors really aren't necessary on a street bike. Downhill racing maybe,or on a tandem. Floating rotors are used extensively on racing cars and motorcycles. The rotor is attached to the wheel by a piece called the carrier. The carrier bolts to the hub and the rotor attaches to the carrier with special mounts that allow it to move slightly. This movement allows the rotor to line up perfectly with the pads for maximum contact area. Mandatory for a 300lbs motorcycle tearing around a track at 180mph,bling on a 30lbs bicycle doing 20 around town.
The $68 rotor is probably made out of better material and will last longer and warp less than the $15 one.