Basic Medicare Part D plans with monthly premiums below the California average are referred to as benchmark plans. The premium for these plans in California is $30.86 in 2012. The full Low-Income Subsidy (LIS) program covers the premium and deductible of benchmark plans. This means you do not pay a premium or deductible if you receive the full LIS benefit and enroll in a benchmark plan. You are, however, still responsible for copayments of $1.10-$6.30 for each covered prescription.
If you enroll in a Medicare Part D plan with premiums higher than the benchmark, you will pay the difference between the subsidy ($30.86) and the plan's premium. See a complete description of plans.