Dude, re-use! Find some other boxes from friends / local shops. Find some packaging from friends / local shops! The CPU needs plenty of padding around it, but can go in a pretty small box, obviously: the monitors provided the screens are well protected and the sides of the box are padded should be fine (maybe rig some holding card to space it out inside the boxes). I’ve shipped a lot of stuff I sold on ebay (a bunch of iBook laptops as well) in this fashion and not only is it recycling, you’ll end up with a more snug custom fit for your item. Good luck!