I got the Surface for around $470 with tax ($450 after student discount + tax), bought the keyboard on eBay new for around $90, and got the pen for sale on Amazon for around $37 if I remember correctly. So all in all I got it for just under $600.
As for the keyboard, it depends on what you're using it for. Don't expect to type out long bodies of text without it. I personally used mine without the keyboard for several months before I spent the extra money for it, but even before I did I loved the thing.
Lastly the 2 GB one is $100 cheaper in the US.