One thing that is not captured accurately in a simple price over parts count computation is the fact that parts complexity is wildly different between shapes. There's a huge difference between a 1x1 plate and a Technic baseplate with holes pointing in every direction, to pick extreme examples.

I believe that even factoring in the extra handling costs and margins, the prices on Pick a Brick give a decent approximation of the actual price span (<$0.10 to >$2.00 per piece).