Average price per weight of new bricks in sets purchased for retail price?
The short answer is that for retail sets, anything under $20 USD per pound of actual parts is a great value. $50 USD per pound appears to be fairly common overall.



I calculated this based on the actual part weights of all parts in a set. I only explored recent Classic, Creator, and City sets as these tend to be a good value and use System bricks almost exclusively. I used recommended retail price and didn't account for sales or other deals that can be found on retail sets.

Here's a graph of recent Classic, Creator, and City sets showing that $50 USD is a reasonable median price per pound:



The best value are the Classic bulk brick boxes, and the worst value per pound are the City minifig sets.