Plastic buoy made from hard plastic, easily available from a hardware shop, costs 4 euros a pop. Circumference 470 mm, diameter 155 mm.
The first is the basket. Guy has used plastic buoys for fishing nets. Drill two holes with a hole-cutter and cut off approximately the back third using a jig-saw. It's advisable to smooth the edges down either using a file, or perhaps by applying a flame. Be careful of fumes, fire, hot dripping plastic though! Some guys have also just taped the edge with duct-tape (called Jesus-teippi in Finnish because it perfoms miracles!).
Super high-tech drawing (NOT!) showing a cross-section of the construction. The "pip" in front of the stick (top left) is the side view of the rim, through which a buoy rope may be passed. Two cross pins are shown to keep the basket in place.
The stick itself is rattan, but hickory or the more traditional ash could also be used. I'm not sure where to source rattan from here in Finland, but Purpleheart Armory stock them, also hickory sticks. Obviously the holes drilled in the basket will depend on which stick material you use. The stick is held in place by drilling a transverse hole at the bottom of the stick and tapping a dowel into the hole. A similar arrangement can also be used at the top of the basket. The models we have (surprise surprise!) though use duct-tape to keep the basket in place above the hand.