many 'thrift shops' have bag sales every now & then- that's when I tend to find the best deals- everything you can fit in a brown paper grocery bag for $5...is the norm around here- I have picked up 15-20 items in one bag easily- it is also a good time to look for wool's- you can fit a number of wools skirts, jackets, jumpers in a bag.
i'm kind of surprised you found Cotton shirts at Kmart. last time I ventured in there was nothing 100% cotton on the shelves/racks. nice score.