Thanks to Angela for this Frugal Baby Tip!
I think I've found the cheapest liners around....
I took a pair of long sleeve, long legged PJ's, that were given as a gift eons ago. I cut it up in to squares. Some are double thickness because they came from the legs/arms. This fabric is pretty thin so its absorbancy is very low, BUT it does its job (keeping poop off the diapers), without bulk.
I doubt if these will last long, as I didn't sew up the edges at all.