You can get an 1,830 CI pack that weighs 22 ounces at REI for $55.

http://www.rei.com/product/747523

That seems right for the smaller scouts. A little above your $40/1lb target but still not too bad. For my son who is 6 I bought the smaller version of this pack (the flash UL) for $25 which weighs 9 ounces and has a capacity of 1000 CI.

For the larger pack how about the Fanatic Fringe Thompson Peak pack which only weighs 9.5 ounces.

http://www.fanaticfringe.com/page5.html

It's 3600 CI for $69 or $79 depending on whether you need the hip belt.