RO units fast enough to run your house are very expensive, i don't know about running plants with softened water, it does run though salt, but not sure exactly what the product is, or why exactly they use salt, may actually look it up...... Anyhow other options to consider, a carbon backwash filter, or just a general whole house filter, not a clean as RO water, but can provide full pressure to your house.
I believe a carbon backwash filter should be about the same as a water softener, not terribly far off, but both are fairly expensive.
A whole house filter starts around $30 goes up from there.
I believe if you want to use RO water for your grow you should get a small 50-100 gallon per day ro filter, and run it to a res (55 gallon barrel is perfect). Run the rest of the house from a different filter. I have a good site for RO systems if you need a link....
Are you on well water or a city tap?