I saw an article in the 2003 Buyer's Guide from Bicycling magazine which attempted to answer the question by comparing a $2,000 bike to a $10,000 bike - and it did a horrible job, if I do say so my self; comparing only the ride characteristics of the bikes and saying nothing about the quality of the materials used or the resulting durability and ease or lack of maintenance. In my continuing pursuit of being your resource for all things cycling - I'll attempt to improve on their comparison.
I'm going to tear apart three bikes (figuratively, not literally) of three distinctly different price levels and tell you just what makes them cost what they do. Hopefully, from there you can choose whether that makes a difference to you - or whether it will require more personal investigation on your part. Which, we will be happy to help you with, of course.
First, to lay the ground work - here's how I'll conduct this comparison.