Patent insurance comes in two basic forms: patent enforcement and patent defense. Enforcement is where someone infringes your patent and you need to enforce your rights. Defense is when someone else accuses you of infringing their patents. This can be a competitor or a patent troll.
Enforcement insurance typically costs about 1% per year of the total amount of insurance. For example, $1,000,000 of patent enforcement insurance will cost about $10,000/year.
Defense insurance typically costs about 3% per year. $1,000,000 of patent defense insurance will cost about $30,000/year.
These amounts are guidelines, and your actual premiums will only be determined after due diligence and underwriting.