Get tubing dies for one. 1 3/4", 1 1/2", 1", and 3/4" can about do it all and then some. There's absolutely no reason to build bumpers out of DOM. 1 3/4 HREW tubing that's got a P&O finish is about $2 a ft countrywide. Most commercially available cages are not DOM and aren't needed to be anyway. Most importantly is get a bender with some kind of attachment to bend the tubing whether air or electric and make the bender sit on wheels. Don't forget the notcher- using a grinder to notch really is terrible and inefficient.