For those willing to add their own rivets, I recently noticed some motorized toy fish in a US discount department store (Target) for about $10US, summer clearance, that I thought looked even more like the Terror fish, about the same size..
Assuming I can still get one and photo it, I'll put up some piccies.
Very impressive, but I don't know how you'd field it (unless you modeled it in dry-dock...).
Obviously, you plop down $100US, and cut it in half...
Doug
Edit: I picked up the toy fish, actually not THAT much a TT, but usable. However, getting an image is problematic. Still working...