DIY Laser Engraver?

I am starting a small business, and would like to engrave my company logo on the products, the box is black, and made of plastic. Anyone have any suggestions for how to build one under $100 out of old CD/DVD-RW Drives? I found this ( https://www.instructables.com/id/Pocket-laser-engraver/?ALLSTEPS ) but dont understand entirely how its built, could anyone give me ideas, or help me understand this post better?

Also, the box is 3x4x1.6 inches, and it needs to be a shallow engravment.

Thanks

What don't you understand. looks like the author lays things out pretty well. May be best to direct your question to the intructable so the author can answer them for you.

+1