Only applies if you have all the power tools needed plus the room in the garage. Also you have to factor in the cost of 1/2 inch CDPVC sheets, not the cheap expanded stuff. Plus unless I'm mistaken, glass is pretty expensive.
But i do agree, you could make them cheaper yourself as you dont have to pay for some other guys time. But heck if you are building your own, just buy a plastic welder and weld your cages like Boaphiles. I do like the welded cages.
And honestly, for the smaller cages, I'm not sure how much cheaper they really are. AP T8s are $150. Thats pretty cheap. A sheet of 4x8 CDPVC would probably cost around $90 and the glass would cost another $50? The bigger cages do get more expensive but again a T25 72x30x18 cage is $399. I imagine that would take at least 2 sheets of CDPVC plus 2x 3 ft glass doors. The killer on the big cages is the shipping. I paid over $300 in shipping for my 3 T25s as they are considered oversize and had to come by freight.