I do my jump shrugs off of 6” and 12” boxes (Range lifting…conditioning the dead area in my pull) with a hex/trap bar w/ bumpers.  Bill’s suggestion with tires is a great and cheap substitution…I’ve made these in the past by welding hubs in the spare tires from some foreign cars keeping the tires small so you can have room for weights.   

The purpose for the bumpers is to jump with the weight and then drop the weight.  I only do positives with no negatives…that means I save myself for the more important aspect of the lift which is the push or pulling phase.  

In my opinion, the hex bar jump shrugs transfer over to the throws more that any other lift in the gym…at least it does for me.  When I get strong jump shrugging my throws take off, especially the weights.