I picked up an Arduino Mega 2560 R3 clone on Ebay for $27.50 and it is definitely worth the money. I was a little concerned that the construction might not be that great because of the price, but it has surprised me, construction is good and soldering is very professional (no cold solder joints that I can see).
My primary development machine is a Ubuntu 12.04 LTS box. Installing the Arduino IDE was easy, I just followed Mark Loiseau’s instructions on his blog. I have been playing with basic sketches and they compile and run great.
Overall, I am very happy with the product.