Don't limit yourself to men's shirts. You may find 100% cotton shirts in your own closet! I have found cute, cute, cute cotton crib sheets at thrift shops as well. It depends on your area but Salvation Army has great buys around here and good sales as well. I use shirts all the time for my charity quilts and have a big tote full of 2.5" strips from cotton shirts ready to use right now! Love sewing green! Reduce, reuse, recycle!

Thanks for the great encouragement!

I live in Buffalo, NY where the vintage sewing machines go for too much also!

I want to emphasize shopping the plus size areas in both men's and women's shirts, There is indeed a lot of fabric in XL shirts and way more in 3X. You can also find plaids in women's clothing, and often in other colors than you find in men's.
I actually used a couple of shirts that were 70/30 cotton/poly because I really wanted the colors in my quilt, and I couldn't tell any difference in the fabrics. I don't think I would use a higher poly content due to the ravelling issue.