Dell Small Business offers its OEM PowerEdge R210 II XL Pentium Dual-Core 2.9GHz Rackmount Server for $905. Coupon code "SAVE356" cuts it to $549. With free shipping, that's $356 off and the lowest total price we could find. It features an Intel Pentium Dual-Core G850 2.9GHz Sandy Bridge processor, 4GB RAM, and 500GB 7200 rpm hard drive. (No optical drive or OS is included.) Deal ends October 23.
Of note, this is an OEM item being sold by Dell and lacks all logos, labels, or other visible branding.