I guarantee you have the supplies to make this in your house RIGHT NOW!! If you don't, it will cost you less than $5 and 5 minutes to make yourself!
What you will need:
Easy Peasy! You will need an apple, rope (you could even use an old lead rope you have lying around) and a knife.
Wash and cut the centre out of the apple (big enough to thread your rope through)
Thread the rope through the apple.
Tie a knot at the end to keep the apple from falling off.
Secure the rope to the ceiling or a bar in your horse's stall.
There you have it!! Cheap AND Easy! And guess what, it will cost you less than most marketed stall toys!