I've had great luck trading unwanted ones on the forums here. Even though some I want are at a second hand shop nearby for $3, Id rather get rid of unwanted ones to trade (they only offer like 25 cents for trade in).
Paying the shipping doesn't matter too much, as domestic costs me a little less than a pre owned dosc and I at least know it's going to someone who wanted it.
Then again I don't try to collect them all, just ones I want and feel I will use.