If you want to learn in an automatic car the chances are you will have to provide the car. This means that you'll need to be insured on the family car from the moment you start learning. If you're driving the instructor's car then you won't need to be insured until you pass or start practising with your parents (which some people don't do).
Why not ask your dad if you can try learning a manual car, some people take to it very easily others need a bit more time. But your dad's estimate sounds very high.
It will cut down your options a lot in the future. If you want to buy an old small car for a few hundred pounds then the number of automatics out there is tiny and they're much more expensive.
Also if you ever need to hire a vehicle you'll be charged extra for auto, if you want to hire an automatic van you'll probably be out of luck. You also might end up in a job where you have to use a company vehicle, which could potentially be problematic.