NEW DELHI/SINGAPORE (Reuters) – Indian budget airline IndiGo has finalised the purchase of 250 A320neo aircraft, Airbus (AIR.PA) said on Monday, handing the European company its biggest-ever order by number of planes in a deal worth $26.55 billion at list prices. The agreement, which Airbus said was signed on Saturday, confirms an earlier provisional order by IndiGo for the 250 narrow-body planes announced in October. IndiGo, which has grown rapidly to become India’s biggest airline by market share, has now ordered 530 A320 family planes from Airbus, the planemaker said in a statement.