I notice that dealers charge very different prices for Arduino hardware. Here I will take the Arduino NANO as an example.
The minimum price was $16 at Ebay, including a mini USB cable and transport from Hong Kong. The maximum price was $57 excluding cable and transport. So don’t spend too much money! The Chinese Arduino has a good quality too.
It seems that $16 for an Arduino NANO is cheap, but that's not the case. It is a simple product in comparison with many other electronics. You can buy already a DVD player for $30. So even an Arduino NANO from $16 is very profitable.