I "repurposed" dd's flannel nighties (she's smaller than me, so I can't wear them) into "new" flannel pillowcases for the entire family. I ended up being able to make 2 out of each gown (Lanz 100 % cotton) and in total, made 9 (odd one was a thrift store nightie that was too narrow to make more than one. I have new dusting rags as well) cases for nothing (the bulk of my thread is inherited from older relatives breaking up their homes).
The cost of a set of flannel cases was $10-$20. I have over 4 new sets so our flannel sheets are extended for yet another winter (keep the house cool at night). The old cases were turned into Swiffer and dusting rags.