When I was a kid, Monogram had a line of kits called "49ers" - they cost $0.49 each and included some pretty cool subjects. My first "expensive" kit was the Monogram Phantom Mustang which cost something like $4.95. I got it as a birthday present with the admonition from my father to take great care in building it because it was so expensive...
Of course back in those days every drug store had an model aisle with kits and a rack of Testors or Pactra paints. Thousands of kids built models back in the 60's.
IMHO the current price levels just reflect a natural progression of the hobby and the economy overall. Certainly manufacturing costs have risen over the years while the pool of modelers has been shrinking.
At the same time modeler's expectations have risen, driving the demand for more detailed, sophisticated state-of-the-art kits.
Just the way it is, I'm afraid. While I never imagined spending $100 on a plastic model kit when I was growing up in the 60's, I also never thought I'd own a $10,000 car or a $100,000 house for that matter...
Mark