I don't think you can find a $1 million umbrella for $60 a year. Typically the umbrella premium is determined by the number and type of exposures you have. If you are a homeowner with 2 autos figure somewhere in the $200/year range for a $1 million umbrella. Add another car, a boat, a rental property, etc. and the premium goes up. It's possible that adding the coverage for the boat on the umbrella ADDED to the base premium of $200, (so the incremental premium was $60 to add the boat).
Your mileage will vary based on driving record, past claims, etc.
Also, you typically have to carry a certain minimum underlying liability limit on your other policies in order to qualify for the umbrella. Typically is it $300k for homeowner or landlord policies, $250/500 for auto, $300k for boat and so forth. If you later lower your limit, lets say to $100k for homeowner, and the insurance company doesn't catch it, here's what would happen. If someone gets a judgement against you for, say, $500,000, your insurance would pay for the first $100,000, then you pay the next $200,000, and then they pay the final $200,000. In essence you have a liability gap from $100k ( your underlying limit) and the minimum underlying limit you are supposed to carry ($300k).