$49.99 (often on sale for $24.99) – but DCS World itself is free with two aircraft (Su-25T and TF-51D). The FC3 module gives you 7 additional jets.
Good news: You don’t need a keygen. The game is widely available at low prices – and sometimes even bundled with modern simulators. Lock On Flaming Cliffs 2 Keygen Indir