Today I learned why saffron costs a little bit more than some other spices. I knew of it as spice that was valued all over the world throughout time, and that it was especially prized in antiquity for colorants in clothing, and for medicine and to season food with--which it is still used for today. I ocassionally buy it because it is considered very healthy, and said to be good for the treatment of vision, depression, high blood pressure and heart disease and many other ailments.
The reason why it's considered a luxury spice however is because it's one of the more labor-intensive ones to extract. It is not harvested in the spring while many things are in bloom, instead the crocus that makes saffron comes from reaches maturity between September and October, and it's at that time saffron is harvested. It has a short window of time to be picked within during the fall also. The crocus--which is an enchanting purple flower, must be plucked after a few hours of the blossom opening, otherwise the stigma of the plant will dry up and become unusable. The color and flavor are all in the stigma. You pick the flower, remove it's stigma and then dry it, and there are your ruby red saffron threads to use as you desire. There's only three threads within one flower though, and I heard from a farmer from India who grows saffron that 55 pounds of flowers are needed to produce half a kilogram of dried saffron.