A cheaper alternative would be fishing line (of the elastic variety). Depending on the gauge and the tension strength, you can also braid it either with itself or into another fiber for added strength.
I have found three possible solutions to this problem.
'Cable organizing' Velcro strips (with one side hook and the other side fuzzy) can be attached to each other to form long adjustable binders. They lack elasticity, however (see solution 3, below)
Elastic bands can be purchased at fabric stores. If cut to length and sewn together into loops, they become ...