Allison,
There consignment shops, resell shops, some factory outlet stores (I usually do not find bargains there often), eBay, service organization donated good stores, stores that are indeed labeled as thrift stores, and the stores that buy closeout clothing lines, or end of season inventory leftovers, or liquidation sale lots - these all can be good sources to save on purchases.
Nordstom Rack is a chain that may have some values for you as well as the traditional clearance racks at many retailers.
One other place to check out are organizations that help people obtain employment. In some larger communities they supply clothing at low cost or even free to women and men who wish to interview for jobs but cannot afford to buy business attire. New York has a "Dress for Success" store where people can donate or obtain clothes for that purpose.
Chrissy