Thats just the printing cost of that one case, getting the 3D files done cost a bomb as well! So this project is well into 4 figures now!
Its just the design of the case itself, the vents only have a few mm each end holding them in place. I think they put supports running across the case as well.. Though a re-design of the "vents" is likely needed anyway.
It may be better to have more of a solid top, with lots of holes, and just the slanted vents to keep the appearance of the original case.