Where can I buy cheap used jeans?

I am getting ready to have a sell out from my boutique with proceeds to go toward charity. Since we are not non-profit, we are not accepting money, nor are we asking for donations from others. We have been blessed to order most of our stuff through liquidation companies. However, I am looking for used cheap clothing, especially jeans. After having lost three family members to cancer and watching my brother and husband battle it, we decided to continue our contribution with these proceeds toward cancer research. This will be my first time doing something like this since opening up in a few months ago. I don't know how my turnout is going to be, but my husband and I are excited. Now, to get to the point. Since my jeans are selling good, please provide me with a site that sells jeans at a reasonable price.