Composting toilets have come a long way.
Forget about water saving toilets. I think no water or composting toilets are the best way to handle human waste. All that manure needs to get back to the earth. There are amazing systems that actually do this. The cost depends on how much work you want to put into it. At the low end is Jenkins' bucket system as described in his book Humanure (available free online). But I could see that taking out buckets of the stuff would get old fast. And it reminds of the untouchables caste, whose job was (and still is in some parts of India) to take out buckets of feces from upper caste homes.
I like the Envirolet. They have normal looking toilets that have a duct that takes the stuff down to a floor below where the composting takes place. The cost is quite high, but then if you compare it to installing a septic tank, it is reasonable. Only problem is getting the building inspector to accept your not putting a septic tank in. There are lots of composting toilets to choose from for example Sun-mar, Biolet, Phoenix, and I believe the Clivus Multrum has been around for a long time.
And then you have to have a system for handling grey water. That will be in another post.