If you have a Big Lots near you, you might want to check for poop-bags there.
They've got them here at this store now for $5 for a package of 120 bags. Normally it's at least $8 for a package that size. They seem to be keeping them in stock too. Colors change every time I go there, but the hanger they're on is always filled with packages.
They tear easy; are as thick as many of the other "premium" brands; fit both our roll dispensers; and that's quite a large savings compared to other places.