P90X2 Medicine Balls
Medicine balls are pretty pricey. But these are about half the price of the Beachbody P90X2 medicine balls.
The Valeo 4 lb. medicine ball has high ratings on Amazon and is available for free shipping (for orders over $35).
Similarly the 8 lb. ball and the 12 lb. ball have high ratings and are cheaper (if not way cheaper) than the Beachbody balls.