The materials aren't really a big factor. The actual materials in a helli are a NEGLIGIBLE part of the cost, manufacturing is where it comes into play, especially with the head and gears etc.. Because you're talking about very small parts that rotate at up to 18-20 THOUSAND RPM on the engine side and 1500-1800 on the rotor head side. It's only semi precision work, but you have to get the parts made by the thousands to make money on them and you have to sell a LOT of helli's to justify that cost. Maybe half or better of the parts in a helli could be made by joe-smoe at a local hobby store. We have a fairly big one out here where you can get brass, steel, stainless, copper, some titanium, rod sheeting angle brackets. All you need is a dremel tool a pair of tin snips and a little bit of junk sheet metal and you can make nearly everything but the head and main shaft parts, add a few screws a little bit of epoxy some super glue, and after some effort you have a helli. Well maybe a lot of effort =>