Other World Computing discounts a selection of used Apple iMacs, MacBooks, Mac minis, and more, with prices starting at $139.
Plus, all orders qualify for free shipping. Each item is covered by a 90-day OWC warranty. Note that for many models, available quantities are limited. A couple best bets:
used Apple iMac Core 2 Duo 1.8GHz 17" 160GB Desktop for $139 ($40 low for a used unit)
used Apple 24" LED-Backlit Cinema Display for $519 ($438 less than a refurb)