PCLiquidations offers the refurbished Dell OptiPlex 790 Intel Core i3 3.1GHz Desktop PC (no monitor) for $79.94 plus about $15 for shipping. Features include:
  • Intel Core i3-2100 3.1GHz dual-core processor
  • 4GB RAM
  • 250GB hard drive
  • CD-ROM drive
Note that it does not ship with an operating system, but you can select one for additional cost. A 90-day warranty applies, but it's unclear who backs it.