Last year, I decided I wanted to make a plaid/striped quilt using a Chunky Churndash pattern (Bonnie Hunter). I scored big time at a garage sale and ended up sitting on the floor with boxes in front of me going through them - I think I paid about $20 for a large paper grocery sack full! It was yardage and certainly a bargain. Then, I got addicted to going to the Goodwill Bin store in our community where they sell for $1.59/lb. I have collected quite a few shirts (always checking that they are 100% cotton) and they immediately go into the washer and dryer (hot cycle). I figure if they survive that, they will survive in a quilt.
I did make queen size Chunky Churndash for my son for Christmas - no idea how many shirts I used but know that I have a lot left to use and my quilting friends and I are setting a date to cut and make up blocks to sew up so we can each have one.