For no-budget/micro budget, insurance ends up being the majority of your budget :)
If this is just for the feature you’re shooting – you want to look into short term insurance for productions under $1 million dollars. I once priced this and it came out to around $700 or so… prices could have changed drastically.
The minimum General Liability insurance requirement for productions is usually $1,000,000 (that’s how much the policy will pay, not how much you pay) but keep an eye out on special requirements from places you want to shoot. I know that shooting on San Diego municipal property, although it’s free, requires $2,000,000.
Beyond that (like the difference between Liability and Workman’s Comp) I’ll avoid answering because I just don’t know enough.