What would it take to have a new large civil aircraft manufacturer?
What are the chances a start-up, with no state money, will come to market with a new 100+ seats plane in the next 20-30 years?


If you count Bombardier, the chances are roughly 100%. The Bombardier C-Series, which will seat 140 (160 max,) is scheduled to enter service within this year (2015.) However, Bombardier is hardly a 'start-up' in the normal sense.


Bombardier C-Series Mock-Up (Source: Wikipedia)

For a real start-up (e.g. a SpaceX-style company,) the chances will be much more slim. It takes billions of dollars worth of investments to design a modern commercial airliner before you will ever see the first dime of revenue. Start-ups generally won't have access to that kind of money until they have had time to mature and developed a steady revenue stream from other successful products (which is how Bombardier is doing it.)


  Could a SpaceX type of company be successful in the airplane manufacturing industry?


That depends greatly on the type of airplanes in question. Undoubtedly, this is possible in the light general aviation market. Several such companies have come and gone over the years. One interesting start-up that is planning to enter production soon is Terrafugia, a start-up from MIT, which is building aircraft that fold up into street-legal cars that can just drive away from the airport and park in your garage. However, the larger airliner market is a completely different ballgame, involving development costs that are orders of magnitude higher. Start-ups have a difficult time getting started in markets with such huge barriers to entry.