Buying an original Mega2560 from Adafruit, Sparkfun, or Arduino will run something like $65 I believe, but you are buying an official Arduino, supporting the original creator, and can have confidence you are buying a reliable board with the correct components installed as opposed to cheaper "alternatives".
The project is open however, and I believe you can buy alternative boards in the $40 price range from places like SainSmart and RepRapDiscount. These boards usually come in different colors and have been rebranded to distinguish them from official Arduino's. I think RepRapDiscount also has made revisions to some models in order to support 24V power supplies.
Finally there are clones. Cheap boards running from $10-$25 with questionable soldering, substitute chips (from what I have read), and didn't even bother changing the silk screen on the boards. In most cases they should be fine and if not, you are still saving money when you buy a second board. The big problem with clones is some people think they are purchasing an Arduino when they are not. In a perfect world, no one would buy the clones / counterfeits until the manufacturers change the silk screening to clarify them as after market or made in china.
The project is open however, and I believe you can buy alternative boards in the $40 price range from places like SainSmart and RepRapDiscount. These boards usually come in different colors and have been rebranded to distinguish them from official Arduino's. I think RepRapDiscount also has made revisions to some models in order to support 24V power supplies.
Finally there are clones. Cheap boards running from $10-$25 with questionable soldering, substitute chips (from what I have read), and didn't even bother changing the silk screen on the boards. In most cases they should be fine and if not, you are still saving money when you buy a second board. The big problem with clones is some people think they are purchasing an Arduino when they are not. In a perfect world, no one would buy the clones / counterfeits until the manufacturers change the silk screening to clarify them as after market or made in china.