If legal in your area, go dumpster diving at local businesses. Try telemarketers, call centers, any place that has 80+ computers is bound to have one break and thrown in the trash needing nothing but a cheap part or some love and attention. That's how I got my first computer ten years ago and it ran fallout wonderfully. Hell, just go to craigslist and look for someone giving away old computers.
EDIT: The comp you need will be easy to come by but to play deus ex you might need to upgrade the video card. 30 bucks max.