By combining 405nm and 532nm, you don't get 473nm, you can get something close to it on the CIE diagram, but it is impossible to get 473, or any other wavelength for that matter.
The main reason for the cost in blue lasers is the crystals needed, as well as the control for the crystals. LBO is a very tough crystal to work with, if you cut it off axis by a couple degrees or even less then a degree, you will greatly decrease the efficiency at a specific temperature. LBO usually needs to be heated to a high temperature and kept there very stable.
Additionally, the gain at the secondary line on Nd:YVO4 or Nd:YAG is much lower which means you need a better cavity, this means less losses on the mirrors, and better anti reflective coatings. The yield on high reflector mirrors, is much lower and thus the lost product makes the cost higher. Antireflective coatings are the same way.