How do you build affordable mountain bike?

If this is about one guy wanting to build himself an affordable bike, then forget it. Getting a whole bike from a yard sale, craigslist, eBay or something like that will be a lot cheaper than buying the parts to build a bike.

If it's about how companies build affordable bikes, well then the answer is in:
  • outsourcing as much as possible of manual production and assembly to countries with low wages
  • getting steep discounts on the bought parts by buying them in huge volumes.