However, I'm not so sure if I would want to put my chips next to a piece of treated wood.

I used to laser engrave items (20 years ago) and there was always residue left over from the vaporized wood. I'm sure that the chemicals to treat the wood would leech on the chips (which would be a very bad thing).

You might think about building the inserts for the chips a little larger to be able to hold the airtite (where that foam rings came from). That way the acids from the wood would only damage the container and not the chip. I would also recommend a hole drilled in the back so you would be able to stick something in there to push out the chip/holder.

I don't think the prices are out of line but I'm sure others can chime in and give you price feedback.

Good luck in you endeavor.