Hop David writes:

Much has been written in this newsgroup how economies of scale could
reduce launch costs.
Recently Ariane ordered 30 Ariane 5 Launchers
http://www.arianespace.com/site/news...ase_index.html
Is 30 enough to enjoy substantial savings due to economy of scale?

Yes, it is. The standard engineering rule of thumb is that unit prices
drop by 30% when the volume doubles. So if you order 32 rather than 8,
the unit price will be only half as much. A factor of 2 is substantial,
though many in this newsgroup think that much larger factors are possible.

Lou Scheffer