One of the things that makes Umbrella insurance so appealing, and almost a no-brainer in most situations, is that the cost is generally very low.
Most insurance carriers offer coverage starting at around $150 per year. The cost of your policy goes up based on the amount of cars and homes you need it to overlay, but in general the cost is pennies on the dollar, and all the risk is on the insurance company.
Even if your premium was $300/yr, the insurance company is on the hook for at least $1,000,000. That is a tremendous value, and something that everyone should think about given the litigious nature of our society.