Just got one Lenovo ThinkCentre "refurbished". For $200, we got C2D @2.6ghz, 4gb RAM, 1TB WD Black HDD, DVD ROM, Windows 7 64 Pro, in compact BTX case. There was no crap installed on it, just plain Windows, ready to go.
Sure, we got crappy keyboard (new), and good MS mouse (used), and couple of scratches on the case. Some puffs with compressed air, and off it went into the shop.
Whether it will last longer - I don't know. If it lasts three years, it will be well paid off for itself. If you gonna buy - just Windows licence is going to cost you $100... But I am more than sure you cannot build anything close to that for $200.