As the plane gets larger the discrepency in price gets considerably exaggerated. You could opt for lower priced esc's and motors besides hacker (think castle creations esc's, axi motors, himaxx motors, etc). this would bring your total cost down.

batteries probably won't drop so fast. these are the same packs in cellphones, camcorders, digital cameras and considering the volume of those industries you would think the prices would drop but for whatever reason they don't fall as fast as regular technology has.