Logitech X-540 5.1 Speaker System for $37.79 after this $15 rebate for purchase made by 3/30.  Shipping is $16.20 so the total comes to $53.99.  Here is a screenshot for your reference.  The system includes 2 front satellite speakers, 2 rear satellite speakers, 1 center satellite speaker, and 1 woofer.  As a comparison, Best Buy currently has it on sale for over $90.
Originally posted earlier, this deal has been revised.