The value of a thing is its contrast to all other things.
Valuable artworks are perhaps a good example of this. What makes the art of Da Vinci valuable is not only its craftsmanship but also its rarity. If I remember correctly less than two dozen works are in existence. For these two reasons his works fetch a premium.
But also how much work is required to produce something will affect the value as well. Something which can be manufactured quickly will mean many are available. So the ubiquity of it brings the value down. And demand too will be dictated by the perceived value of something will also change its value.
Value is a complex and changing thing.