i made my own, i can explain you how but all what helped me is google
is used 2 bungee cords and elastic rope which goes between two bungee cords
also i used tennis balls putting one in head height and one for body punching, i made holes in the middle of balls and put rope through them, looped rope on a bungee cord hook and thats it.
upper bungee cord hook is in the ceiling, downer is in the base on the floor.
i made base of two 4kg dumbbells connected with some ropes..
^ this links helped me a lot