Anyone who has a band saw usually has a bunch of these, and just haven’t gotten around to throwing them away yet, so you can get them for free.
Then, bend them like in these images (here, they are used for painting, but it would work well as a laser bed thing as well). Bend them into any shape needed for your project. They are steel, so they won’t even reflect as much as an aluminium honeycomb.
Edit: Thanks for adding image tags!