The price goes up on materials that become scarce. Some, like gas, go up and down in response to price futures, political or economic policy. The gas can be stored at a low price but you will pay the price determined by the prevailing price at present.
I don't think that 'scacity' is even a word. Dictionary.com does not think it is. Neither does Word or even the wiki.answers.com editor
Scarcity means shortage.
Water scacity
It means only a limited amount of items has been produced therefor limit of goods and services will be produced
That depends on certain factors. These factors include scacity of the products, demand for the product, is the product in good shape, and is the product a popular figure that has value? These are simple questions but there are many more. Check with your local comic book store or toy dealer for more information.