If you qualify for a subsidy
Covered California is the most affordable coverage available, full stop. Medicaid is expanded (Medi-Cal) in California.
If you don't
Full-price marketplace plans are the most expensive coverage in California. For healthy people, private PPOs on Cigna, Aetna and PHCS PPO are routinely 30–50% less. California has its own individual mandate: residents without qualifying coverage owe a penalty on their state return.
What's not affordable
Health-sharing ministries and indemnity plans look cheap until you have a claim. Ask for the out-of-pocket maximum; if there isn't one, it isn't insurance.
California regulates non-ACA coverage more tightly than most states, and the state mandate and Covered California's state subsidies change the math for many people, so private options here are narrower and the honest answer is often a careful comparison, not a promise of savings.