I think it definitely makes sense to out source for these one off's.
What's the difference really between them hiring, training someone and buying all the hardware and dedicating factory floor space to it and getting these experts to do it? The end result will no doubt be the same.
Hell, they can probably do it better, it's what they specialise in.
I'm sure PRS want to keep their overheads down, and aren't these guy's very local to PRS anyway?