I agree with marcelo. Tissue culture is the most sustainable way to make plants available en masse. However, it is time consuming and not always successful (just like lab flasking). Obviously the nurseries would need to cover the cost of their laboratories and other necessities. High price is arguable, as it really depends on rarity of species. We must remember that these nurseries are still a business and theur main aim is profit, so they cater mostly to serious hobbyists that are able to pay big bucks for a rare item. How would they survive by mass cloning nep truncata 'black' and selling it for USD$1?
They also need to eat, you know...