I received a few samples of essential oils from Eden Botanicals a US company located in Hyampom, California. The samples included: Sandalwood, Lemon, Lavender and a tiny Sample of Jasmine Absolute.
The samples included a note about how each oil was collected, its place of origin and the plant part that contains the essential oil. In the case of the tiny sample of Jasmine, the oil is collected from the flowers. In the case of lemon the oil is collected from the peels. The potency of these oils is impressive, I can distinctly smell each one through the tiny sample vial without opening it. Since the samples were shipping in clear containers I have been storing them in a dark spot in my home where the light won't reach them.
Certain methods of extractions are more costly then others but these costly methods help preserve more of the plants essential oils. These things help determine the cost of the oil. The Jasmine for example is a more expensive oil so the sample size was much smaller than the Lemon, Sandalwood or Lavender oil.
I recommend stocking up on some oils because not only to they offer terrific aromatherapy benefits but certain oils also have medicinal properties. Tea tree for example is a powerful antiseptic... Thyme oil is a wonderful disinfectant. Look to Eden Botanicals as a source for pure wholesale essential oils and even rare ones!