I purchases my spray starch on line. I like the "Faithless Quilting & Crafting trigger bottle better than anything I have found. It's about $9 a bottle, but it does go a long ways and I don't think I use as much of it to get the fabric ready to quilt. Some of the quilt shops care it, but it's usually higher price.
That is what I bought by the gallon at MSQC. I have noticed no build up at all on the iron or on my ironing pad. I spray the fabric generously and press before cuttings.