Your message here is heartbreaking and hits home for me personally. I have a family member who similarly married a completely horrible and miserable person who seems to fit the mold of your stepmother. I'm not all that great at responding to the message boards but I wanted to because of your response. My highest and best suggestion for affordable San Diego housing is get onto Craigslist as there are always roommate opportunities.
I am lifetime native San Diegan and know everywhere in and around here well so if you want specific area info, etc feel free to bounce questions off of me as I'd be happy to provide you directions and help.
You're going to like living in San Diego. I can tell you that much. I truly hope your situation works out.
Good luck to you, I hope you find something soon.