Frogman , the CX insurance covers 15,000 HK but some of the car hire companies will charge you up to £2500 which still can leave you £1000 in the hole .
Story from many years ago, a friend took the hire car back with a tiny scratch which could have been easily fixed , He was told that his credit card would be charged £1000 to cover the damage . " What would I be charged if I had totalled it he asked ?" The same amount , its the excess you know, its what you agreed to on the contract .
He still had the keys and hadn't yet closed the contract , so he jumped into the car did a few doughnuts in the parking lot , smashed the rear side into a lamp post threw the keys at the agent and walked away with a lot more than £1000 damage which was what he was immediately charged on his credit card. So yes the repair costs are ludicrous.
Some advice I received, take photos of all sides of the car when you take it , if its dark use a torch , check the spare tyre and tools , take another set of pictures when you hand it back , especially important if you are dropping it after hours because its the only recourse that you have for disputed charges, also take pictures of the mileage and tyres . The rental agency has already ring fenced the excess amount from your card so they are more than happy to deduct money from your account
there is a broker in UK that deals with rental cars and offers additional excess insurance at reasonable rates which is worth looking at , I am not endorsing them in anyway shape or form but if you ( enjoy car hire ) do a google search with wording in brackets you should find it .
Just a word of caution a number of the travel insurance policies are only valid for 30 days from commencement of travel so if you are more than that you may not be covered