Thanks, abeltino!
Meantime, I have found in "Gas Turbine World 1997 Handbook", page 26, for a CCP close to may needs (396.0MW) a value of $380/kW, so not so close to $250/kW, but also a notice that "depending on scope pf equipment, site specific requrements, geographic location and competitive market location, THESE PRICES CAN VARY CONSIDERABLY" (for this reasons I need some assumptions) => did somebody know an useful web link with the above info or have a fresh info from the above book?