Hi Demented,
... this are good and very precise DC-gearhead-motors ...
If you have to by them at the manufacturers, you pay from 50$ to 500$ (or even more, when smaller and more accurate), but when scaveaged, the price drops mostly to a fraction - i sometimes found good motors for a tenth of the original price.
Or for example my 3D-CNC-system: once it was sold for nearly 12.000DM (~6.000