I second thrift shopping. Although, I don't tell coworkers that I do it. I guess I fear the stigma of being "found out" wearing secondhand clothes. It's never bothered me, but I'm leery of being judged. I'm terribly proud of some of my thrift shop "scores", though! I've often been complimented on my outfits and wonder what they would think if they knew I paid $6 each for the shirt and skirt or $10 for the dress!
It is hit and miss, but with a little patience and a lot of looking, you can find brand names (some brand new!) I often find Jones New York, Chico's, Talbots, Anne Klein, etc. Mostly, I shop at Goodwill. Here's a little hint. If you find something you like in your size, look closely at all the nearby racks. It means that someone with your taste and shape has brought in a load of clothes for donation, and if there's one item, there are bound to be more.
Congratulations on needing to purchase new clothes! And, happy hunting!