That really depends on your definition of "cheap" and "efficient". With the hardware you have, a relatively inexpensive upgrade would be to undervolt your Core2Duo or Pentium 4 and then pair it up with a GTX 450, 460, 550Ti, or 560 for 9000-13000PPD average at modest power consumption. Getting a CPU+motherboard+RAM to get the same 9000+ PPD would be more expensive than the GPUs I mentioned. You'll need to use Windows though because of the GPU folding.
If you have a budget in mind and know how much you'll tolerate on your electric bill, then we can help you with a decision.
__________________ "The computer programmer says they should drive the car around the block and see if the tire fixes itself." [src] |