REI has used gear sales, a garage sale now and then and you can also check geartrade.com.  You may also find items in Craigs list and Facebook.  Remember if you go the used route to validate the quality of the item and that it still has some hiking life left in it.  Good luck.  

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.