I can buy RO for $0.44 a gallon that has beer measuring 3 ppm TDS, pretty nice, and that is used for light lagers. The other source is $0.27 a gallon, and is 45 TDS, so that is used for ales. Some of the difference is the feed water, the second being on a city with wells, and the other would be the RO system filters life cycle point.
The local brewpub has let me get nano filtered water at 13 ppm which is pretty good!