Having umbrella insurance coverage added to your current insurance policy costs between $150.00 to $300.00 per year depending on the amount of coverage you want.
I have umbrella insurance along with my current insurance policy through Progressive insurance and pay $200.00 per year which to me is worth it.
Progressive umbrella insurance is the cheapest I've found and I would highly recommend Progressive Insurance for auto insurance, homeowners insurance etc and for the umbrella insurance.
State Farm Insurance has cheap umbrella insurance as well and I would recommend them too because I had them before but I found Progressive to be cheaper.
Both Progressive Insurance and State Farm Insurance companies are good insurance companies.