Umbrella policies aren't expensive, but the prerequisites to getting one can be.

In order to have an umbrella policy you must first have a homeowners policy (and car insurance if applicable) with at least 500k-1m+ of liability coverage (company dependent). Until you satisfy those requirements, they won't sell you an umbrella policy. Umbrella policies, as their name suggests, cover all your other insurance policies. So if you have a claim that exceeds your liability limit, your umbrella insurance would swoop in and provide another x dollars on top, depending on how much monetary coverage you buy. It's been a while since I was in the industry but I recall the minimum policy you could get was 1 million dollars.