we have several thrift stores where I live. My "favorite" has shirts for $1.. all shirts, long sleeve, short sleeve, t-shirts, mens, womens, cotton, flannel, etc... all $1. I've found I can find unique fabrics by purchasing thrift store shirts than going to fabric stores. I had to have orange and white gingham check for a project and the only thing I could find was a poly/cotton blend so I went to my favorite shop. There were 3 different color orange/white cotton gighams!
I think at our Good Will men's dress shirts are $4.99 but I keep an eye on the clearance rack and on $1 day, I can get a mens button down for $1.