According to their site, each $14 filter would get him about 3.75 gallons of filtered water. They mention something like 22.5 gallons life for 200 TDS.

If his dissolved solids aren't ionic, he might be better with a regular old carbon filter or a 3 stage under the sink. With ionic contaminants, filtration even on a large scale is expensive (I used to use deionized water; you get a big tank for a filter, the size of a scuba tank, but it's pricey and I don't know the cost comparison).

The first thing to do is sample your water and send it off to get a water profile. Find out what's in it.