Bitcoins value is dependant on the intensity of demand and supply there is. The demand is a market factor. The intensity with which the market needs the commodity fuels the demand aspect. Supply however is a limited factor within the Bitcoin economy since the number of bitcoins there can exist within the network is limited to 21 Million.
There isnt any actual set price for a Bitcoin. The price of Bitcoin is a balance between what price someone is willing to trade with to part from the Bitcoin.