Not that I grow carnivorous plants, but if they are sensitive to minerals, wouldn't distilled water work well? You can buy it by the gallon at any grocery store. (I use it both for ironing and for soap making.) While it is inexpensive enough, I don't know how the cost would compare to the reverse osmosis water.

Around here one gal of distilled will cost around a dollar. I can fill a 5 gal jug for $1.50. But you are correct. Distilled water will work fine