I ditto what Nammie to 7 said... The Pellon SF101 is a great product to have around! It is great for what you're looking to do here.. But it's also my favorite stabilizer for making bags ... If one layer isn't quite enough, a double layer works beautifully.
When half my bolt is gone, I start watching the sales... & usually buy mine when Joann's is having any 40-50% off sale... I call in and order a full bolt.