TigerDirect offers the refurbished HP DC5800 Pentium Dual-Core 2GHz Desktop PC model no. RB-825633304215, for $79.99 plus $9.54 for shipping. That's $70 off and the lowest total price we could find. It features an Intel Pentium E2180 2GHz dual-core processor, 2GB RAM, 250GB hard drive, DVD/CD-RW combo drive, and Windows 7 Home Premium 32-bit. A 1-year Joy Systems warranty applies.
Don't mind a slightly smaller hard drive? Newegg offers a similar build, but with a 160GB hard drive, for $87.99 with free shipping.