You have to remember, Aurisonics uses 3D printing to make their shells. The result is a body that won't be polished. To polish it, they have to do additional work and maybe even use additional materials (their housings are not acrylic or silicone, I can't say what it is though). Other CIEM companies use acrylic which comes out polished. So they don't have to do anything to make it polished... IDK what the process is to polish the materials they use, but if it is complex enough (and I can see reason why it is), it would cost 250 bucks.
If you asked a CIEM company to add an unsmooth texture, a light, microscopic fingerprint texture on their shells (this is what Aurisonics has if I'm not mistaken), they will charge you for it. However, that's the default that Aurisonics does... for free...
EDIT: I got ninja'd :p Read the post above me, it's an official word from Dale :)
I think Dale uses an SLA machine. If I'm right, the resin he uses should cost quite a lot.