As it should happen the weight to price ratio varies across all types of pasta sold by Amazon. Long noodles that can be efficiently boxed seem to be the cheapest, followed by the short stubby ones that can be boxed kind of efficiently, followed by the weird-shaped ones, and then the stuffed ones.
Generally I lean toward long noodles, so I ended up purchasing regular ol' spaghetti. If I find myself in the mood for penne at some point, I can always get a 4lbs bag at a local Costco-type place.