I don't know, never bought one premade.
Let me think...
Tray, rez, stand, pump, flood fittings (inlet, overflow) - sized to the outlet of the pump, probably 1/2" but check pump description to make sure, timer, airstones, airpump... (aquarium/pet stores have 'em). Bam you're good. Make the stand 5" taller than the rez, basic table shape but about 30" square on top, that's just right to prevent the tray from sagging in the middle or on the edges like the one in your link will.
One thing - 50l of hydroton isn't enough to fill the tray. Unless you've got huge spaces between the pots it takes about 100L for me to do one tray.