Simple and no where near the cost of a composting toilet.

We have a cabin annex outhouse. The outhouse has a box with a regular toilet seat on top. Underneath is a bucket. Outside is a pen made out of 4 pallets on end. Each time you go, scoop plenty of sawdust in the bucket. Once the bucket is full, the contents go in the pen: put down a layer of straw, dump the bucket, cover with more straw. Rinse the bucket with soapy water. Repeat.

If you use enough sawdust, there is no smell.

(The guy who introduced it to us used it for a family of 5. The contents of the pen break down fast enough that it took them a couple of years before a 2nd one was needed.)