IMHO, you may want to consider 4" square w/side brackets for ease of access with mud rings, as opposed to a 3-1/2" deep device box. It's faster to get in to bond, and a little wider on the sides. Easier to work with IMO, but either way, the $$ is much more than plastic boxes.
Include $$ for bonding the boxes. Green screws, pigtails, etc.
What reasoning did the HO give for metal boxes?? He may change his mind seeing the price.
It is rare,very rare to see metal boxes in resi.
