You could easily build it, but that's if you have the tools and supply stores to do it. I doubt for half, but maybe 2/3's the cost. Home Depot sheetmetal will cost 3X what a metal supply store would cost. Then bending, my metal brake was over $200 for the cheapest 36" one I could find. Then you would have to think of a thermal cutoff switch or thermal dimmer switch, incase you forget to plug in your fans. I have done this with a water-cooled fixture I built and it is the only 2 COB's I have fried, to date.