@EmoPanda : Can you afford the $30 (after shipping) tri-top ? It's much more durable than elastic. If you get the $3/y elastic (which is the kind you need), the price will add up quickly and you'll probably need at least 5 yards.
It's important to not just wrap the elastic AROUND you. You have to have the elastic angled to press *down and sideways* on the breasts. If you just wrap around, the pressure needed to bind can quickly become too great and can easily cause pain/injuries.
@Chaletica, binding depends a lot on how "squishy" you are - breast tissue varies person to person - some people can easily compress a D cup with only a sports bra since their breasts are relatively "squishy", while some can't get a B cup to go down without more. You could try on sports' bras in a store and see if they work - and if they don't, don't buy them and look for a real binder.