Commercial composting toilets are very expensive, up to $20,000 for a unit powerful enough for an entire family. Good news though, there are clever ways to compost human manure much cheaper.
One of the best known ways of processing your own human waste is the humanure system, which is laid out in great detail in the Humanure Handbook, an absolutely excellent manual that I highly recommend to anyone interested in taking their personal nutrient cycle into their own hands.
The humanure system uses simple five gallon buckets, lots of sawdust, and outdoor pallet compost bins to create a safe, healthy, odour-free system of human waste processing. Waste is deposited in a five gallon bucket (I would highly recommend lining the bucket with newspaper before-hand) and covered with sawdust after the deposit has been made. Once the bucket is full, it is carried outside to the pallet composters and dumped to allow to compost for at least a year.
Left: Simple five gallon bucket toilet. This one comes with enzyme packets which will presumably aid in the composting speed of human waste.
See more information on this particular toilet system.