IIRC all the chips were about $100 per unit, but of course that depended on the quantity that I was building (~120). When I looked at it briefly, it looked like I might be able to get the BOM price down to $50-70/unit if I made 1k-10k units.

There was a ton of manual assembly for each unit (some due to my errors, some due to the PCBA's errors, some simply due to the design of the device). All in all, it's not get-rich-quick/ever scheme haha.