Think
this costs more. 1 meter beams!
He was saying price per output
Though I know of a cheaper source for 501nm. CNI! Only about $4999
Even cheaper, argon. Multilines or tunable will do 496 and 501.7 in <5mW output for a twentieth the cost of that unit.
Supply and demand. There is very little demand from a credible source (non-hobbyist). This means that in order to get one, you need to pay a lot of money for the company to reroute their production, and probably stop their mass production lines, just to coat a handful of mirrors, and then cherry pick the right ones.
This is a very complicated SHG wavelength. This isn't something you will get from your regular production mirror.
So they make yellows, greens, and blues all day long. All of a sudden an order comes in needing coatings for 946 and 1064 for an SHG process, and you need resonance of 500.77. Well now what?!
They must stop the presses, change out the coatings and equipment, do a few runs, and sift through for the perfect mirrors since this is a VERY low gain, and voila! You have your 500.77nm labby, for $8k (or $5k from CNI).
All about supply and demand
EDIT: Yeah, what he said! ^