PC Balls of Steel edition is $22 at amazon
http://www.amazon.com/Duke-Nukem-Forever-Balls-Edition-Pc/dp/B002I0HL98/ref=sr_1_2?ie=UTF8&qid=1338784533&sr=8-2
You'll need a 650W minimum power supply to ensure you don't ruin it when you're playing games with maxed out graphics. Someone feedback-ed they had a 520W but that's really unwise.
Best Buy has the keyboard alone for $39.99. Clearance item, availability may vary and applies to the Xbox 360, Wii and PS3. Just tossing that in here...
In store only