This is how most of us get our RO water.
This system is about $139 and is a great deal even if you are just using it for drinking water. My water is 400 PPM out of the tap, it goes to 7 PPM after this filter. I put in replacement filters when my PPMs go to 50 (about every two years). The replacement filter kit runs about $60.
It will pay for it's self in drinking water. The arrowhead drinking water we used to buy tests at 150 ppm (tap water).
If you can't mount a unit under the sink, you can buy a portable unit for about $75.
The under the sink ones are much better and a hell of a lot faster (if given the choice).