I'm trying to decide whether it means "something is wrong" when adding USB multiplies the price of the thing by five.
its a little more complex than that. first off its a double-sided pre-assembled PCB. that adds quite a bit of cost. secondly, its a 4-layer board, which is more expensive to fab & test than a 2-layer. the nano (like the lilypad) is an Arduino, and so they both have to pay a licensing fee (5%-10%). and lastly, paul doesn't factor in a retailers margin. when you consider -all- of the costs, it is clear how the price ends up at $50!
the nano is good design.