You should be able to recoup your costs on ebay easily I'd wager
Remember, start with a good foundation, a good pump (Iwaki is excellent if money's not a problem, otherwise eheim in my experience is also very good). The new Swiftech MCP600 pump is getting good recommendations, and seems to be a well built, powerful pump, which runs of 12v to boot. So you can run it off the PC PSU without worries. (That's what I'd get if I was starting from scratch)
CPU block you can make, or purchase for $40-50. Rad heater cores are also good and the cheapest of the three main components (pump, cpu block and rad), once you have these three main costly components then you're in business. Keep us posted on your progress.