By the early 1920s, small airlines were struggling to compete, and there was a movement towards increased rationalization and consolidation. In 1924, Imperial Airways was formed from the merger of Instone Air Line Company, British Marine Air Navigation, Daimler Airway and Handley Page Transport Co Ltd., to allow British airlines to compete with stiff competition from French and German airlines that were enjoying heavy government subsidies. The airline was a pioneer in surveying and opening up air routes across the world to serve far-flung parts of the British Empire and to enhance trade and integration.
At the same time, Juan Trippe began a crusade to create an air network that would link America to the world, and he achieved this goal through his airline, Pan American World Airways, with a fleet of flying boats that linked Los Angeles to Shanghai and Boston to London. Pan Am and Northwest Airways (which began flights to Canada in the 1920s) were the only U.S. airlines to go international before the 1940s.
Among the first countries to have regular airlines in Latin America and the Caribbean were Bolivia with Lloyd Aéreo Boliviano, Cuba with Cubana de Aviación, Colombia with Avianca (the first airline established in the Americas), Argentina with Aerolineas Argentinas, Chile with LAN Chile (today LATAM Airlines), Brazil with Varig, Dominican Republic with Dominicana de Aviación, Mexico with Mexicana de Aviación, Trinidad and Tobago with BWIA West Indies Airways (today Caribbean Airlines), Venezuela with Aeropostal, Puerto Rico with Puertorriquena; and TACA based in El Salvador and representing several airlines of Central America (Costa Rica, Guatemala, Honduras and Nicaragua). All the previous airlines started regular operations well before World War II. Puerto Rican commercial airlines such as Prinair, Oceanair, Fina Air and Vieques Air Link came much after the second world war, as did several others from other countries like Mexico's Interjet and Volaris, Venezuela's Aserca Airlines and others.
Most airlines use differentiated pricing, a form of price discrimination, to sell air services at varying prices simultaneously to different segments. Factors influencing the price include the days remaining until departure, the booked load factor, the forecast of total demand by price point, competitive pricing in force, and variations by day of week of departure and by time of day. Carriers often accomplish this by dividing each cabin of the aircraft (first, business and economy) into a number of travel classes for pricing purposes.
You’d have to check the schedule for your specific dates but I think Santorini then Milos then Paros then Naxos and Athens would probably be the best order. 3 days in each sounds great. Or a small tweak: 2 days in Milos and then 4 days in Santorini (splitting time between 2 of the 4 caldera towns) or even 4 days in Paros (splitting time between Naousa and Parikia).
Excellent choice of islands, though getting between them presents one or two challenges (they are not as conveniently connected like the Cycladic or Dodecanese islands so island hopping is not as popular in this island group). All three islands are served by airports with year-round connections to Athens and in the Summer with international charter flights from Europe. Let’s take the pros and cons of each island.