Nathan of InsideMicrosoft deconstructs Amazon's recent 1,000 XBOX 360s for $100 each promotion in "Xbox 360 Promotion Crashes Amazon".
Amazon servers crashed for about 12 minutes during the promotion (roughly until the units were sold out).
In short, based on average volumes, Amazon lost $200,000 in revenue from the sale of a $300 device at $100 and around $242,000 in lost revenue from sales missed during the 12-minute 'crash'.
However, Amazon gained HUGE promotional value for this event; the $442,000 could easily be justified in a Marketing budget.