CA Backyard 400 sq ft cottage for handicapped man under $10k HUD

[Melody Rosenberg]

I am a senior and own a home in California. I need to get a one bedroom or studio cottage installed to HUD standards for my mentally handicapped adult son. It needs to be 400 sq ft or smaller, very basic, and $10k. Does anyone know where this can be found in CA. Our building department is difficult to work with. I have been searching the web with no luck.