I'll tell you how to get shock cord for cheap!
Step 1: Obtaining Cheap Shock Cord
It happens to all of us. We build an Esties model rocket, launch it a dozen times and then the shock cord gets ripped/burned. Esties sells replacement cord for $$. Many people don't realize that shock cord is actually 1/4" elastic, which you can purchase at any fabric store. Better yet, it's available in the sewing/craft section of your local Wal-Mart.