starting to wonder about your psychic powers now...
Yes, the dealer wanted £299 for 3 years.
I've found a couple of better deals on the interwebs (not looking very hard yet as I can't buy the policy until I get the car) AND one of them said I could defer the start of the cover by up to a year. This is awesome because, as you said, my regular car insurance will replace with a brand new one for the first year, so I'm not spending money double-covering myself. Example quote for that was £84 (which they call "vehicle replacement", £64 for "combined Return to Invoice GAP" and I can't honestly see a difference at this point) for the three years. The car is on a 4-year finance deal, so potentially at the end of that I'd be replacing it anyway.
I'm still trying to work out the difference between GAP and RTI, but I think
from what I've read and what you said, that GAP pays the difference between the insurance claim and the remaining amount on finance (so I end up with no cash in hand and nothing more to pay back), but RTI is against the original value of the car, so it costs more, but you also receive more money (enough for a deposit for a new car, perhaps?).
Of course, touch wood, I'd never need it. But that's the nature of insurance.