I totally agree that $/HP is a poor comparison or yard stick.
It make more sense to use that type thing when comparing modifications or bolt-ons that are for increasing the power on an engine that's already together.
The car rags are great at doing a $150 mod (CC just did this very thing) to gain less than 1 HP.
They swapped carb bodies to make a 650 a 750, to gain something like .6 (as in 6/10) HP! It could have just as easily LOST .6 HP depending on the dyno, if they'd have made another pull...
Not a very good return on the money spent. But to hear them tell it, all was just dandy- ProForm being an advertiser and all.