The "batting tape" is very expensive and the roll is very narrow, 1-1/2"??. My LQS owner suggested to use the thin woven interfacing, the one with the tiny white dots on one side. She sells it for $1/yd and is 60" wide. I have purchased and used same and it works well and obviously, it is a lot cheaper.
I fold and pin the edges together and when I need, I just whack off 2", move the pins for next time. -- Use a medium hot iron w/or w/o steam. Works for me.