Good point!
1. A way to do it all for less is to find the minimum size and clearances, then install bathroom paneling that looks like linoleum on the walls. This will keep mold to a minimum if you have any at all.
2. Then install only a toilet, a floor dran and a cold water sink.
3. Make your shower portable: fill a heavy plastic or food grade 55 gallon drum with water, then use a small immersion heater to heat it. Use a 12VDC pump to pump hot water from the 55 gal drum that you mix with cold water faucet using a T-hose.
4. The floor drain takes care of the water, and it dries quicly, especially in the summer, or if you squeegee it.
I plan on doing this in my garage as soon as I finish the insulation and inside shelf building phase.
Right now I have a warm-as-toast 20 x 30 inside workshop that is insulated to R-38 and even has insulated mats on the nfloor. The rest of the garage is a 50 x 30 space that is being insulated with shelving and new electrical installed.
Then next year, when my pension check arrives, it will be time for a well and septic.