You can build a pretty decent computer with a small budget. But if you really want to cut costs, the folks at Linus Tech Tips scrounged together a used server motherboard, two tandem quad-core CPUs, and 16GB of RAM for under $US150 ($209).
Of course, the full rig will cost a bit more than that (you'll still need a case, GPU, and power supply), but under $250 for eight cores and 16GB of RAM is one of the most stellar values we've ever seen. And according to Linus' benchmarks, it works pretty darn well as a cheap gaming rig.
However, building with old server components isn't a cakewalk. Finding compatible parts is a bit of a hassle, and you may have to do a bit of DIY modding to make everything work together properly. Linus, for example, had to saw off a piece of his graphics card to make it fit, and use a piece of wood as a CPU cooler backplate. Still, the final product is impressive for the price.
Is it actually worth doing? Well...that depends on how much your time is worth to you. But as with all things DIY, half the glory comes from the success of a build that works despite the odds, and this certainly falls into that category. Check out the video for all the gory details.
Under $US150 ($209) Budget Gaming 8 Core CPU, Motherboard & 16GB RAM [Linus Tech Tips]