like rob - i'd work on what materials cost plus what he usually charges ph or whatever. then she takes it and he's got extra work or she doesn't and he's no worse off...
if they're cheaper elsewhere than he can make then he won't want to undercut his usual price just to get the work .
He might want to point out though that his are tailor made to the artwork sizes and also what sort of materials - shipping to US you'll want strong wood not some flimsy stuff thats going to break first time the carrier throws crate across room ( and they do folks - all the time

a courier friend said they have xx hours to unload and reload xx crates of parcels - what they do is stand and unload and as they do they don't carefully carry eat work to next lorry/crate - even if covered in fragile stickers - they throw them in the right direction and go over and load when there's a decent pile there...)