550 Cord Bracelets:
They are cheap, don't take long to make, useful, and (somewhat) stylish.
What you need:
10 Feet of cord per bracelet. It is sold in various lengths but cheapest if you buy it by the 1,000 ft spool.
550 Cord: http://www.supplycaptain.com/index.cfm?fus...;category_ID=19
Side Release Buckle (Not necessary but I use them and think they give the bracelet a more 'professional' look.
Again the prices vary depending on how many you buy.
http://cdwplus.com/singleSRB.html
I have accumulated quite a selection of both over time but if you buy 100 buckles ($30) and 1,000 Ft of 550 cord ($48) your price per bracelet comes to under $1 each even with shipping included. These take a little practice to get down but after you make a few your brain gets used to the repitition and you can make them while watching tv, riding in the car, etc.
And finally, here is a pretty good set of instructions on how to make these.
http://www.raems.com/550_cord_bracelet.pdf