Other World Computing discounts a selection of used Apple Mac Pros, with prices starting at $619. Plus, all orders qualify for free shipping. Each item is covered by a 90-day OWC warranty. Note that for some models, available quantities may be limited. A couple best bets:

• Used Apple Mac Pro Quad 2.66GHz Xeon Workstation for $649 (pictured, $97 low for used)
• used Apple Mac Pro 8-Core Xeon 2.93GHz Workstation w/ 16GB RAM for $1,379 ($220 low)