Depends on if they are wild caught or farm bred. I saw a site selling a 12cm one for $500.
WC Blue Zaires are expensive because they are found deeper in Lake Tanganyika. For this reason it takes about 5 days to bring them up to the surface to collect. Alot of time and effort goes into collecting them.
Here is an explanation I found on another site as to why they are expensive: The high price of the Zaire blue is determined by a series of factors. First and foremost is the fact that a great distance must be covered to reach the closest airport. The fish must be caught twice as deep and are much wilder and thus more vulnerable to stress. Moreover the geographic region in which they occur is politically very unstable. Catching and thus diving to depths of 40 meters carries with it much greater risks for the divers and the bottom time is much shorter. For this reason, twice as many people are involved in this effort. When you add all these factors up, it surprises me every time when wild-caught Zaire blue frontosas are available for sale. At one point I calculated what it would cost if a fish such as this were to be caught in Europe under these conditions, including personnel costs, insurance, fuel, and costs of the risk involved, and it worked out to NLG 1700 to 2000 (approx. US $740 to $865 at the current exchange rate) per fish!