Best Buy has the Gaiam Restore Heavy Resistance Cord w/ Door Attachment (Blue, 05-62223) on clearance for $7.99 with free in-store pickup or  free shipping with My Best Buy (free to join). Also on sale:

• Gaiam Restore Medium Resistance Cord w/ Door Attachment for $5.49
• Gaiam Restore Light Resistance Cord w/ Door Attachment for $5.49