Can you drop employer sponsored health plan if you cannot afford it?

Yes, you can drop it. You are not required to maintain health coverage or maintain any specific health coverage. Contact your HR department for the terms of your contract to determine how you go about dropping coverage. Most employers only allow such a change during open enrollment periods.

Note, C1peterka's response has been moved to the discussion section, as it contains advice and opinion regarding the subject rather than an answer to the question.